| Message ID | 1557398877-32750-1-git-send-email-wang.yi59@zte.com.cn (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,next] KVM: lapic: allow set apic debug dynamically | expand |
On Thu, May 09, 2019 at 06:47:57PM +0800, Yi Wang wrote: > There are many functions invoke apic_debug(), which is defined > a null function by default, and that's incovenient for debuging > lapic. > > This patch allows setting apic debug according to add a apic_dbg > parameter of kvm. > > Signed-off-by: Yi Wang <wang.yi59@zte.com.cn> > --- > v2: change apic_dbg to bool and tag __read_mostly. Thanks to Sean. > > arch/x86/kvm/lapic.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 9bf70cf..0827e7c 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -54,8 +54,13 @@ > #define PRIu64 "u" > #define PRIo64 "o" > > +static bool apic_dbg __read_mostly; > +module_param(apic_dbg, bool, 0644); Probably don't need to shorten "debug". > + > /* #define apic_debug(fmt,arg...) printk(KERN_WARNING fmt,##arg) */ > -#define apic_debug(fmt, arg...) do {} while (0) > +#define apic_debug(fmt, arg...) do { if (apic_dbg) \ > + printk(KERN_DEBUG fmt, ##arg); \ > +} while (0) Pulling in your comment regarding sched_debug and noirqdebug... On Thu, May 09, 2019 at 08:29:38AM +0800, wang.yi59@zte.com.cn wrote: > Also, we have some similar parameters already, such like sched_debug, > noirqdebug :) The IRQ debug hook is a completely different beast than the APIC debug messages. sched_debug is a much better comparison. The param only exists if CONFIG_SCHED_DEBUG=y, which is "default y" but "depends on DEBUG_KERNEL". That seems like the route to go if we want the ability to toggle APIC debugging at runtime. And if we go with an all encompassing config, e.g. CONFIG_KVM_DEBUG, we can use it to wrap x86/mmu.c's debug param as well (and rename it to mmu_debug). > > /* 14 is the version for Xeon and Pentium 8.4.8*/ > #define APIC_VERSION (0x14UL | ((KVM_APIC_LVT_NUM - 1) << 16)) > -- > 1.8.3.1 >
On Fri, May 10, 2019 at 12:54:21PM +0800, wang.yi59@zte.com.cn wrote: > I grep "debug" in arch/x86/kvm, and find these *_debug: > ioapic_debug > apic_debug > > and dbg in mmu.c, which is better to be renamed to mmu_debug as you said. > > and vcpu_debug, which uses kvm_debug macro. > > kvm_debug macro uses pr_debug which can be dynamically set during running > time, so, how about change all *_debug in kvm to pr_debug like vcpu_debug? It's still the same end result, we're bloating and slowing KVM with code and conditionals that aren't useful in normal operation. grep vcpu_debug a bit further and you'll see that the only uses in x86 are when the guest has crashed, is being reset, or is accessing an unhandled MSR and KVM is injecting a #GP in response. In other words, the existing uses are only in code that isn't remotely performance critical. hyperv.c: vcpu_debug(vcpu, "hv crash (0x%llx 0x%llx 0x%llx 0x%llx 0x%llx)\n", hyperv.c: vcpu_debug(vcpu, "hyper-v reset requested\n"); x86.c: vcpu_debug_ratelimited(vcpu, "unhandled wrmsr: 0x%x data 0x%llx\n", x86.c: vcpu_debug_ratelimited(vcpu, "unhandled rdmsr: 0x%x\n", pr_debug does have more direct uses, notably in nested VMX and KVM TSC handling. Similar to the above vcpu_debug case, the nVMX uses are all failing paths and not performance critical. The TSC code does have one path that may affect performance (get_kvmclock_ns()->kvm_get_time_scale()), but I don't think that should be considered as setting the precedent. In fact, it may make sense to convert the TSC pr_debugs to be gated by CONFIG_DEBUG_KVM as well. Paolo, do you have any thoughts?
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 9bf70cf..0827e7c 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -54,8 +54,13 @@ #define PRIu64 "u" #define PRIo64 "o" +static bool apic_dbg __read_mostly; +module_param(apic_dbg, bool, 0644); + /* #define apic_debug(fmt,arg...) printk(KERN_WARNING fmt,##arg) */ -#define apic_debug(fmt, arg...) do {} while (0) +#define apic_debug(fmt, arg...) do { if (apic_dbg) \ + printk(KERN_DEBUG fmt, ##arg); \ +} while (0) /* 14 is the version for Xeon and Pentium 8.4.8*/ #define APIC_VERSION (0x14UL | ((KVM_APIC_LVT_NUM - 1) << 16))
There are many functions invoke apic_debug(), which is defined a null function by default, and that's incovenient for debuging lapic. This patch allows setting apic debug according to add a apic_dbg parameter of kvm. Signed-off-by: Yi Wang <wang.yi59@zte.com.cn> --- v2: change apic_dbg to bool and tag __read_mostly. Thanks to Sean. arch/x86/kvm/lapic.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)