| Message ID | 53770380-053e-70b6-f75e-a0e00bf35c30@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [next,v2] softirq: enable MAX_SOFTIRQ_TIME tuning with sysctl, max_softirq_time_msecs | expand |
Friendly ping ... On 2019/6/25 11:13, Zhiqiang Liu wrote: > From: Zhiqiang liu <liuzhiqiang26@huawei.com> > > In __do_softirq func, MAX_SOFTIRQ_TIME was set to 2ms via experimentation by > commit c10d73671 ("softirq: reduce latencies") in 2013, which was designed > to reduce latencies for various network workloads. The key reason is that the > maximum number of microseconds in one NAPI polling cycle in net_rx_action func > was set to 2 jiffies, so different HZ settting will lead to different latencies. > > However, commit 7acf8a1e8 ("Replace 2 jiffies with sysctl netdev_budget_usecs > to enable softirq tuning") adopts netdev_budget_usecs to tun maximum number of > microseconds in one NAPI polling cycle. So the latencies of net_rx_action can be > controlled by sysadmins to copy with hardware changes over time. > > Correspondingly, the MAX_SOFTIRQ_TIME should be able to be tunned by sysadmins, > who knows best about hardware performance, for excepted tradeoff between latence > and fairness. Here, we add sysctl variable max_softirq_time_msecs to replace > MAX_SOFTIRQ_TIME with 2ms default value. > > Note: max_softirq_time_msecs will be coverted to jiffies, and any budget > value will be rounded up to the next jiffies, which relates to CONFIG_HZ. > The time accuracy of jiffies will result in a certain difference > between the setting jiffies of max_softirq_time_msecs and the actual > value, which is in one jiffies range. > > Signed-off-by: Zhiqiang liu <liuzhiqiang26@huawei.com> > --- > Documentation/sysctl/kernel.txt | 17 +++++++++++++++++ > kernel/softirq.c | 8 +++++--- > kernel/sysctl.c | 9 +++++++++ > 3 files changed, 31 insertions(+), 3 deletions(-) > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index f0c86fbb3b48..23b36393f150 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -44,6 +44,7 @@ show up in /proc/sys/kernel: > - kexec_load_disabled > - kptr_restrict > - l2cr [ PPC only ] > +- max_softirq_time_msecs > - modprobe ==> Documentation/debugging-modules.txt > - modules_disabled > - msg_next_id [ sysv ipc ] > @@ -445,6 +446,22 @@ This flag controls the L2 cache of G3 processor boards. If > > ============================================================== > > +max_softirq_time_msecs: > + > +Maximum number of milliseconds to break the loop of restarting softirq > +processing for at most MAX_SOFTIRQ_RESTART times in __do_softirq(). > +max_softirq_time_msecs will be coverted to jiffies, and any budget > +value will be rounded up to the next jiffies, which relates to CONFIG_HZ. > +The time accuracy of jiffies will result in a certain difference > +between the setting jiffies of max_softirq_time_msecs and the actual > +value, which is in one jiffies range. > + > +max_softirq_time_msecs is a non-negative integer value, and setting > +negative value is meaningless and will return error. > +Default: 2 > + > +============================================================== > + > modules_disabled: > > A toggle value indicating if modules are allowed to be loaded > diff --git a/kernel/softirq.c b/kernel/softirq.c > index a6b81c6b6bff..1e456db70093 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -199,7 +199,8 @@ EXPORT_SYMBOL(__local_bh_enable_ip); > > /* > * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, > - * but break the loop if need_resched() is set or after 2 ms. > + * but break the loop if need_resched() is set or after > + * max_softirq_time_msecs msecs. > * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in > * certain cases, such as stop_machine(), jiffies may cease to > * increment and so we need the MAX_SOFTIRQ_RESTART limit as > @@ -210,7 +211,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); > * we want to handle softirqs as soon as possible, but they > * should not be able to lock up the box. > */ > -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) > +unsigned int __read_mostly max_softirq_time_msecs = 2; > #define MAX_SOFTIRQ_RESTART 10 > > #ifdef CONFIG_TRACE_IRQFLAGS > @@ -248,7 +249,8 @@ static inline void lockdep_softirq_end(bool in_hardirq) { } > > asmlinkage __visible void __softirq_entry __do_softirq(void) > { > - unsigned long end = jiffies + MAX_SOFTIRQ_TIME; > + unsigned long end = jiffies + > + msecs_to_jiffies(max_softirq_time_msecs); > unsigned long old_flags = current->flags; > int max_restart = MAX_SOFTIRQ_RESTART; > struct softirq_action *h; > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 1beca96fb625..96ff292ce7f6 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -118,6 +118,7 @@ extern unsigned int sysctl_nr_open_min, sysctl_nr_open_max; > #ifndef CONFIG_MMU > extern int sysctl_nr_trim_pages; > #endif > +extern unsigned int max_softirq_time_msecs; > > /* Constants used for minimum and maximum */ > #ifdef CONFIG_LOCKUP_DETECTOR > @@ -1276,6 +1277,14 @@ static struct ctl_table kern_table[] = { > .extra2 = &one, > }, > #endif > + { > + .procname = "max_softirq_time_msecs", > + .data = &max_softirq_time_msecs, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &zero, > + }, > { } > }; >
Friendly ping ... On 2019/6/28 14:52, Zhiqiang Liu wrote: > Friendly ping ... > > On 2019/6/25 11:13, Zhiqiang Liu wrote: >> From: Zhiqiang liu <liuzhiqiang26@huawei.com> >> >> In __do_softirq func, MAX_SOFTIRQ_TIME was set to 2ms via experimentation by >> commit c10d73671 ("softirq: reduce latencies") in 2013, which was designed >> to reduce latencies for various network workloads. The key reason is that the >> maximum number of microseconds in one NAPI polling cycle in net_rx_action func >> was set to 2 jiffies, so different HZ settting will lead to different latencies. >> >> However, commit 7acf8a1e8 ("Replace 2 jiffies with sysctl netdev_budget_usecs >> to enable softirq tuning") adopts netdev_budget_usecs to tun maximum number of >> microseconds in one NAPI polling cycle. So the latencies of net_rx_action can be >> controlled by sysadmins to copy with hardware changes over time. >> >> Correspondingly, the MAX_SOFTIRQ_TIME should be able to be tunned by sysadmins, >> who knows best about hardware performance, for excepted tradeoff between latence >> and fairness. Here, we add sysctl variable max_softirq_time_msecs to replace >> MAX_SOFTIRQ_TIME with 2ms default value. >> >> Note: max_softirq_time_msecs will be coverted to jiffies, and any budget >> value will be rounded up to the next jiffies, which relates to CONFIG_HZ. >> The time accuracy of jiffies will result in a certain difference >> between the setting jiffies of max_softirq_time_msecs and the actual >> value, which is in one jiffies range. >> >> Signed-off-by: Zhiqiang liu <liuzhiqiang26@huawei.com> >> --- >> Documentation/sysctl/kernel.txt | 17 +++++++++++++++++ >> kernel/softirq.c | 8 +++++--- >> kernel/sysctl.c | 9 +++++++++ >> 3 files changed, 31 insertions(+), 3 deletions(-) >> >> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt >> index f0c86fbb3b48..23b36393f150 100644 >> --- a/Documentation/sysctl/kernel.txt >> +++ b/Documentation/sysctl/kernel.txt >> @@ -44,6 +44,7 @@ show up in /proc/sys/kernel: >> - kexec_load_disabled >> - kptr_restrict >> - l2cr [ PPC only ] >> +- max_softirq_time_msecs >> - modprobe ==> Documentation/debugging-modules.txt >> - modules_disabled >> - msg_next_id [ sysv ipc ] >> @@ -445,6 +446,22 @@ This flag controls the L2 cache of G3 processor boards. If >> >> ============================================================== >> >> +max_softirq_time_msecs: >> + >> +Maximum number of milliseconds to break the loop of restarting softirq >> +processing for at most MAX_SOFTIRQ_RESTART times in __do_softirq(). >> +max_softirq_time_msecs will be coverted to jiffies, and any budget >> +value will be rounded up to the next jiffies, which relates to CONFIG_HZ. >> +The time accuracy of jiffies will result in a certain difference >> +between the setting jiffies of max_softirq_time_msecs and the actual >> +value, which is in one jiffies range. >> + >> +max_softirq_time_msecs is a non-negative integer value, and setting >> +negative value is meaningless and will return error. >> +Default: 2 >> + >> +============================================================== >> + >> modules_disabled: >> >> A toggle value indicating if modules are allowed to be loaded >> diff --git a/kernel/softirq.c b/kernel/softirq.c >> index a6b81c6b6bff..1e456db70093 100644 >> --- a/kernel/softirq.c >> +++ b/kernel/softirq.c >> @@ -199,7 +199,8 @@ EXPORT_SYMBOL(__local_bh_enable_ip); >> >> /* >> * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, >> - * but break the loop if need_resched() is set or after 2 ms. >> + * but break the loop if need_resched() is set or after >> + * max_softirq_time_msecs msecs. >> * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in >> * certain cases, such as stop_machine(), jiffies may cease to >> * increment and so we need the MAX_SOFTIRQ_RESTART limit as >> @@ -210,7 +211,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); >> * we want to handle softirqs as soon as possible, but they >> * should not be able to lock up the box. >> */ >> -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) >> +unsigned int __read_mostly max_softirq_time_msecs = 2; >> #define MAX_SOFTIRQ_RESTART 10 >> >> #ifdef CONFIG_TRACE_IRQFLAGS >> @@ -248,7 +249,8 @@ static inline void lockdep_softirq_end(bool in_hardirq) { } >> >> asmlinkage __visible void __softirq_entry __do_softirq(void) >> { >> - unsigned long end = jiffies + MAX_SOFTIRQ_TIME; >> + unsigned long end = jiffies + >> + msecs_to_jiffies(max_softirq_time_msecs); >> unsigned long old_flags = current->flags; >> int max_restart = MAX_SOFTIRQ_RESTART; >> struct softirq_action *h; >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c >> index 1beca96fb625..96ff292ce7f6 100644 >> --- a/kernel/sysctl.c >> +++ b/kernel/sysctl.c >> @@ -118,6 +118,7 @@ extern unsigned int sysctl_nr_open_min, sysctl_nr_open_max; >> #ifndef CONFIG_MMU >> extern int sysctl_nr_trim_pages; >> #endif >> +extern unsigned int max_softirq_time_msecs; >> >> /* Constants used for minimum and maximum */ >> #ifdef CONFIG_LOCKUP_DETECTOR >> @@ -1276,6 +1277,14 @@ static struct ctl_table kern_table[] = { >> .extra2 = &one, >> }, >> #endif >> + { >> + .procname = "max_softirq_time_msecs", >> + .data = &max_softirq_time_msecs, >> + .maxlen = sizeof(unsigned int), >> + .mode = 0644, >> + .proc_handler = proc_dointvec_minmax, >> + .extra1 = &zero, >> + }, >> { } >> }; >> > > > . >
Friendly ping... On 2019/6/25 11:13, Zhiqiang Liu wrote: > From: Zhiqiang liu <liuzhiqiang26@huawei.com> > > In __do_softirq func, MAX_SOFTIRQ_TIME was set to 2ms via experimentation by > commit c10d73671 ("softirq: reduce latencies") in 2013, which was designed > to reduce latencies for various network workloads. The key reason is that the > maximum number of microseconds in one NAPI polling cycle in net_rx_action func > was set to 2 jiffies, so different HZ settting will lead to different latencies. > > However, commit 7acf8a1e8 ("Replace 2 jiffies with sysctl netdev_budget_usecs > to enable softirq tuning") adopts netdev_budget_usecs to tun maximum number of > microseconds in one NAPI polling cycle. So the latencies of net_rx_action can be > controlled by sysadmins to copy with hardware changes over time. > > Correspondingly, the MAX_SOFTIRQ_TIME should be able to be tunned by sysadmins, > who knows best about hardware performance, for excepted tradeoff between latence > and fairness. Here, we add sysctl variable max_softirq_time_msecs to replace > MAX_SOFTIRQ_TIME with 2ms default value. > > Note: max_softirq_time_msecs will be coverted to jiffies, and any budget > value will be rounded up to the next jiffies, which relates to CONFIG_HZ. > The time accuracy of jiffies will result in a certain difference > between the setting jiffies of max_softirq_time_msecs and the actual > value, which is in one jiffies range. > > Signed-off-by: Zhiqiang liu <liuzhiqiang26@huawei.com> > --- > Documentation/sysctl/kernel.txt | 17 +++++++++++++++++ > kernel/softirq.c | 8 +++++--- > kernel/sysctl.c | 9 +++++++++ > 3 files changed, 31 insertions(+), 3 deletions(-) > > diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt > index f0c86fbb3b48..23b36393f150 100644 > --- a/Documentation/sysctl/kernel.txt > +++ b/Documentation/sysctl/kernel.txt > @@ -44,6 +44,7 @@ show up in /proc/sys/kernel: > - kexec_load_disabled > - kptr_restrict > - l2cr [ PPC only ] > +- max_softirq_time_msecs > - modprobe ==> Documentation/debugging-modules.txt > - modules_disabled > - msg_next_id [ sysv ipc ] > @@ -445,6 +446,22 @@ This flag controls the L2 cache of G3 processor boards. If > > ============================================================== > > +max_softirq_time_msecs: > + > +Maximum number of milliseconds to break the loop of restarting softirq > +processing for at most MAX_SOFTIRQ_RESTART times in __do_softirq(). > +max_softirq_time_msecs will be coverted to jiffies, and any budget > +value will be rounded up to the next jiffies, which relates to CONFIG_HZ. > +The time accuracy of jiffies will result in a certain difference > +between the setting jiffies of max_softirq_time_msecs and the actual > +value, which is in one jiffies range. > + > +max_softirq_time_msecs is a non-negative integer value, and setting > +negative value is meaningless and will return error. > +Default: 2 > + > +============================================================== > + > modules_disabled: > > A toggle value indicating if modules are allowed to be loaded > diff --git a/kernel/softirq.c b/kernel/softirq.c > index a6b81c6b6bff..1e456db70093 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -199,7 +199,8 @@ EXPORT_SYMBOL(__local_bh_enable_ip); > > /* > * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, > - * but break the loop if need_resched() is set or after 2 ms. > + * but break the loop if need_resched() is set or after > + * max_softirq_time_msecs msecs. > * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in > * certain cases, such as stop_machine(), jiffies may cease to > * increment and so we need the MAX_SOFTIRQ_RESTART limit as > @@ -210,7 +211,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); > * we want to handle softirqs as soon as possible, but they > * should not be able to lock up the box. > */ > -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) > +unsigned int __read_mostly max_softirq_time_msecs = 2; > #define MAX_SOFTIRQ_RESTART 10 > > #ifdef CONFIG_TRACE_IRQFLAGS > @@ -248,7 +249,8 @@ static inline void lockdep_softirq_end(bool in_hardirq) { } > > asmlinkage __visible void __softirq_entry __do_softirq(void) > { > - unsigned long end = jiffies + MAX_SOFTIRQ_TIME; > + unsigned long end = jiffies + > + msecs_to_jiffies(max_softirq_time_msecs); > unsigned long old_flags = current->flags; > int max_restart = MAX_SOFTIRQ_RESTART; > struct softirq_action *h; > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 1beca96fb625..96ff292ce7f6 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -118,6 +118,7 @@ extern unsigned int sysctl_nr_open_min, sysctl_nr_open_max; > #ifndef CONFIG_MMU > extern int sysctl_nr_trim_pages; > #endif > +extern unsigned int max_softirq_time_msecs; > > /* Constants used for minimum and maximum */ > #ifdef CONFIG_LOCKUP_DETECTOR > @@ -1276,6 +1277,14 @@ static struct ctl_table kern_table[] = { > .extra2 = &one, > }, > #endif > + { > + .procname = "max_softirq_time_msecs", > + .data = &max_softirq_time_msecs, > + .maxlen = sizeof(unsigned int), > + .mode = 0644, > + .proc_handler = proc_dointvec_minmax, > + .extra1 = &zero, > + }, > { } > }; >
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index f0c86fbb3b48..23b36393f150 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -44,6 +44,7 @@ show up in /proc/sys/kernel: - kexec_load_disabled - kptr_restrict - l2cr [ PPC only ] +- max_softirq_time_msecs - modprobe ==> Documentation/debugging-modules.txt - modules_disabled - msg_next_id [ sysv ipc ] @@ -445,6 +446,22 @@ This flag controls the L2 cache of G3 processor boards. If ============================================================== +max_softirq_time_msecs: + +Maximum number of milliseconds to break the loop of restarting softirq +processing for at most MAX_SOFTIRQ_RESTART times in __do_softirq(). +max_softirq_time_msecs will be coverted to jiffies, and any budget +value will be rounded up to the next jiffies, which relates to CONFIG_HZ. +The time accuracy of jiffies will result in a certain difference +between the setting jiffies of max_softirq_time_msecs and the actual +value, which is in one jiffies range. + +max_softirq_time_msecs is a non-negative integer value, and setting +negative value is meaningless and will return error. +Default: 2 + +============================================================== + modules_disabled: A toggle value indicating if modules are allowed to be loaded diff --git a/kernel/softirq.c b/kernel/softirq.c index a6b81c6b6bff..1e456db70093 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -199,7 +199,8 @@ EXPORT_SYMBOL(__local_bh_enable_ip); /* * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, - * but break the loop if need_resched() is set or after 2 ms. + * but break the loop if need_resched() is set or after + * max_softirq_time_msecs msecs. * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in * certain cases, such as stop_machine(), jiffies may cease to * increment and so we need the MAX_SOFTIRQ_RESTART limit as @@ -210,7 +211,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); * we want to handle softirqs as soon as possible, but they * should not be able to lock up the box. */ -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) +unsigned int __read_mostly max_softirq_time_msecs = 2; #define MAX_SOFTIRQ_RESTART 10 #ifdef CONFIG_TRACE_IRQFLAGS @@ -248,7 +249,8 @@ static inline void lockdep_softirq_end(bool in_hardirq) { } asmlinkage __visible void __softirq_entry __do_softirq(void) { - unsigned long end = jiffies + MAX_SOFTIRQ_TIME; + unsigned long end = jiffies + + msecs_to_jiffies(max_softirq_time_msecs); unsigned long old_flags = current->flags; int max_restart = MAX_SOFTIRQ_RESTART; struct softirq_action *h; diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 1beca96fb625..96ff292ce7f6 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -118,6 +118,7 @@ extern unsigned int sysctl_nr_open_min, sysctl_nr_open_max; #ifndef CONFIG_MMU extern int sysctl_nr_trim_pages; #endif +extern unsigned int max_softirq_time_msecs; /* Constants used for minimum and maximum */ #ifdef CONFIG_LOCKUP_DETECTOR @@ -1276,6 +1277,14 @@ static struct ctl_table kern_table[] = { .extra2 = &one, }, #endif + { + .procname = "max_softirq_time_msecs", + .data = &max_softirq_time_msecs, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = &zero, + }, { } };