Message ID | e4d42bda-72f2-4002-f319-1cbe2bff74d2@huawei.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | arm64: psci: Use udelay() instead of msleep() to reduce waiting time | expand |
From: Yunfeng Ye > Sent: 11 September 2019 09:50 > We want to reduce the time of cpu_down() for saving power, found that > cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail. > > Normally the time cpu dead is very short, it is no need to wait 10ms. > so use udelay 10us to instead msleep 10ms in every waiting loop, and add > cond_resched() to give a chance to run a higher-priority process. > > Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> > --- > arch/arm64/kernel/psci.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c > index 85ee7d0..9e9d8a6 100644 > --- a/arch/arm64/kernel/psci.c > +++ b/arch/arm64/kernel/psci.c > @@ -86,15 +86,15 @@ static int cpu_psci_cpu_kill(unsigned int cpu) > * while it is dying. So, try again a few times. > */ > > - for (i = 0; i < 10; i++) { > + for (i = 0; i < 10000; i++) { > err = psci_ops.affinity_info(cpu_logical_map(cpu), 0); > if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) { > pr_info("CPU%d killed.\n", cpu); > return 0; > } > > - msleep(10); > - pr_info("Retrying again to check for CPU kill\n"); > + cond_resched(); > + udelay(10); You really don't want to be doing 10000 udelay(10) before giving up. If udelay(10) is long enough for the normal case, then do that once. After that use usleep_range(). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On 2019/9/12 16:48, David Laight wrote: > From: Yunfeng Ye >> Sent: 11 September 2019 09:50 >> We want to reduce the time of cpu_down() for saving power, found that >> cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail. >> >> Normally the time cpu dead is very short, it is no need to wait 10ms. >> so use udelay 10us to instead msleep 10ms in every waiting loop, and add >> cond_resched() to give a chance to run a higher-priority process. >> >> Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> >> --- >> arch/arm64/kernel/psci.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c >> index 85ee7d0..9e9d8a6 100644 >> --- a/arch/arm64/kernel/psci.c >> +++ b/arch/arm64/kernel/psci.c >> @@ -86,15 +86,15 @@ static int cpu_psci_cpu_kill(unsigned int cpu) >> * while it is dying. So, try again a few times. >> */ >> >> - for (i = 0; i < 10; i++) { >> + for (i = 0; i < 10000; i++) { >> err = psci_ops.affinity_info(cpu_logical_map(cpu), 0); >> if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) { >> pr_info("CPU%d killed.\n", cpu); >> return 0; >> } >> >> - msleep(10); >> - pr_info("Retrying again to check for CPU kill\n"); >> + cond_resched(); >> + udelay(10); > > You really don't want to be doing 10000 udelay(10) before giving up. > > If udelay(10) is long enough for the normal case, then do that once. > After that use usleep_range(). > > David > Thanks for your advice. the delay depend on the num of cores, range from 50us to 500us, I have test the time on the 140+ cores cpu: (10us every time) [ 1177.979642] psci: CPU1 killed. total wait 4 times [ 1178.011369] psci: CPU2 killed. total wait 6 times [ 1178.035247] psci: CPU3 killed. total wait 3 times [ 1178.071134] psci: CPU4 killed. total wait 8 times ...... [ 1190.128202] psci: CPU139 killed. total wait 50 times [ 1190.156266] psci: CPU140 killed. total wait 48 times [ 1190.192082] psci: CPU141 killed. total wait 46 times [ 1190.224104] psci: CPU142 killed. total wait 46 times Can I bust-wait 1ms,which is 100 tiems udelay(10), after that, use usleep_range(1000, 10000) ? I don't want other process occupy cpu for a long time when I let out the cpu. thanks. > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c index 85ee7d0..9e9d8a6 100644 --- a/arch/arm64/kernel/psci.c +++ b/arch/arm64/kernel/psci.c @@ -86,15 +86,15 @@ static int cpu_psci_cpu_kill(unsigned int cpu) * while it is dying. So, try again a few times. */ - for (i = 0; i < 10; i++) { + for (i = 0; i < 10000; i++) { err = psci_ops.affinity_info(cpu_logical_map(cpu), 0); if (err == PSCI_0_2_AFFINITY_LEVEL_OFF) { pr_info("CPU%d killed.\n", cpu); return 0; } - msleep(10); - pr_info("Retrying again to check for CPU kill\n"); + cond_resched(); + udelay(10); } pr_warn("CPU%d may not have shut down cleanly (AFFINITY_INFO reports %d)\n",
We want to reduce the time of cpu_down() for saving power, found that cpu_psci_cpu_kill() cost 10ms after psci_ops.affinity_info() fail. Normally the time cpu dead is very short, it is no need to wait 10ms. so use udelay 10us to instead msleep 10ms in every waiting loop, and add cond_resched() to give a chance to run a higher-priority process. Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com> --- arch/arm64/kernel/psci.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)