* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() [not found] ` <20190628011012.GA19488@lerouge> @ 2019-10-23 8:16 ` Wanpeng Li 2019-10-23 8:29 ` Thomas Gleixner 0 siblings, 1 reply; 6+ messages in thread From: Wanpeng Li @ 2019-10-23 8:16 UTC (permalink / raw) To: Thomas Gleixner Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker On Fri, 28 Jun 2019 at 09:10, Frederic Weisbecker <frederic@kernel.org> wrote: > > On Fri, Jun 28, 2019 at 08:43:12AM +0800, Wanpeng Li wrote: > > From: Wanpeng Li <wanpengli@tencent.com> > > > > On a machine, cpu 0 is used for housekeeping, the other 39 cpus in the > > same socket are in nohz_full mode. We can observe huge time burn in the > > loop for seaching nearest busy housekeeper cpu by ftrace. > > > > 2) | get_nohz_timer_target() { > > 2) 0.240 us | housekeeping_test_cpu(); > > 2) 0.458 us | housekeeping_test_cpu(); > > > > ... > > > > 2) 0.292 us | housekeeping_test_cpu(); > > 2) 0.240 us | housekeeping_test_cpu(); > > 2) 0.227 us | housekeeping_any_cpu(); > > 2) + 43.460 us | } > > > > This patch optimizes the searching logic by finding a nearest housekeeper > > cpu in the housekeeping cpumask, it can minimize the worst searching time > > from ~44us to < 10us in my testing. In addition, the last iterated busy > > housekeeper can become a random candidate while current CPU is a better > > fallback if it is a housekeeper. > > > > Cc: Ingo Molnar <mingo@redhat.com> > > Cc: Peter Zijlstra <peterz@infradead.org> > > Cc: Frederic Weisbecker <frederic@kernel.org> > > Cc: Thomas Gleixner <tglx@linutronix.de> > > Signed-off-by: Wanpeng Li <wanpengli@tencent.com> > > Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Hi Thomas, I didn't see your refactor to get_nohz_timer_target() which you mentioned in IRC after four months, I can observe cyclictest drop from 4~5us to 8us in kvm guest(we offload the lapic timer emulation to housekeeping cpu to avoid timer fire external interrupt on the pCPU which vCPU resident incur a vCPU vmexit) w/o this patch in the case of there is no busy housekeeping cpu. The score can be recovered after I give stress to create a busy housekeeping cpu. Could you consider applying this patch for temporary since I'm not sure when the refactor can be ready. Wanpeng ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() 2019-10-23 8:16 ` [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() Wanpeng Li @ 2019-10-23 8:29 ` Thomas Gleixner 2019-10-23 9:25 ` Wanpeng Li 2020-01-06 6:21 ` Wanpeng Li 0 siblings, 2 replies; 6+ messages in thread From: Thomas Gleixner @ 2019-10-23 8:29 UTC (permalink / raw) To: Wanpeng Li Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker On Wed, 23 Oct 2019, Wanpeng Li wrote: > I didn't see your refactor to get_nohz_timer_target() which you > mentioned in IRC after four months, I can observe cyclictest drop from > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to > housekeeping cpu to avoid timer fire external interrupt on the pCPU > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of > there is no busy housekeeping cpu. The score can be recovered after I > give stress to create a busy housekeeping cpu. > > Could you consider applying this patch for temporary since I'm not > sure when the refactor can be ready. Yeah. It's delayed (again).... Will pick that up. Thanks, tglx ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() 2019-10-23 8:29 ` Thomas Gleixner @ 2019-10-23 9:25 ` Wanpeng Li 2020-01-06 6:21 ` Wanpeng Li 1 sibling, 0 replies; 6+ messages in thread From: Wanpeng Li @ 2019-10-23 9:25 UTC (permalink / raw) To: Thomas Gleixner Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker On Wed, 23 Oct 2019 at 16:29, Thomas Gleixner <tglx@linutronix.de> wrote: > > On Wed, 23 Oct 2019, Wanpeng Li wrote: > > I didn't see your refactor to get_nohz_timer_target() which you > > mentioned in IRC after four months, I can observe cyclictest drop from > > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to > > housekeeping cpu to avoid timer fire external interrupt on the pCPU > > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of > > there is no busy housekeeping cpu. The score can be recovered after I > > give stress to create a busy housekeeping cpu. > > > > Could you consider applying this patch for temporary since I'm not > > sure when the refactor can be ready. > > Yeah. It's delayed (again).... Will pick that up. Sorry, you will pick up the patch or refactor? :) Wanpeng ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() 2019-10-23 8:29 ` Thomas Gleixner 2019-10-23 9:25 ` Wanpeng Li @ 2020-01-06 6:21 ` Wanpeng Li 2020-01-10 14:12 ` Thomas Gleixner 1 sibling, 1 reply; 6+ messages in thread From: Wanpeng Li @ 2020-01-06 6:21 UTC (permalink / raw) To: Thomas Gleixner Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker Hi Thomas, On Wed, 23 Oct 2019 at 16:29, Thomas Gleixner <tglx@linutronix.de> wrote: > > On Wed, 23 Oct 2019, Wanpeng Li wrote: > > I didn't see your refactor to get_nohz_timer_target() which you > > mentioned in IRC after four months, I can observe cyclictest drop from > > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to > > housekeeping cpu to avoid timer fire external interrupt on the pCPU > > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of > > there is no busy housekeeping cpu. The score can be recovered after I > > give stress to create a busy housekeeping cpu. > > > > Could you consider applying this patch for temporary since I'm not > > sure when the refactor can be ready. > > Yeah. It's delayed (again).... Will pick that up. I didn't find WIP tag for this work after ~half year since v4 was posted https://lkml.org/lkml/2019/6/28/231 Could you apply this patch for temporary because the completion time of refactor is not deterministic. Wanpeng ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() 2020-01-06 6:21 ` Wanpeng Li @ 2020-01-10 14:12 ` Thomas Gleixner 2020-01-13 1:32 ` Wanpeng Li 0 siblings, 1 reply; 6+ messages in thread From: Thomas Gleixner @ 2020-01-10 14:12 UTC (permalink / raw) To: Wanpeng Li Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker Wanpeng, Wanpeng Li <kernellwp@gmail.com> writes: > Hi Thomas, > On Wed, 23 Oct 2019 at 16:29, Thomas Gleixner <tglx@linutronix.de> wrote: >> >> On Wed, 23 Oct 2019, Wanpeng Li wrote: >> > I didn't see your refactor to get_nohz_timer_target() which you >> > mentioned in IRC after four months, I can observe cyclictest drop from >> > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to >> > housekeeping cpu to avoid timer fire external interrupt on the pCPU >> > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of >> > there is no busy housekeeping cpu. The score can be recovered after I >> > give stress to create a busy housekeeping cpu. >> > >> > Could you consider applying this patch for temporary since I'm not >> > sure when the refactor can be ready. >> >> Yeah. It's delayed (again).... Will pick that up. > > I didn't find WIP tag for this work after ~half year since v4 was > posted https://lkml.org/lkml/2019/6/28/231 Could you apply this patch > for temporary because the completion time of refactor is not > deterministic. Could you please repost it? Thanks, tglx ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() 2020-01-10 14:12 ` Thomas Gleixner @ 2020-01-13 1:32 ` Wanpeng Li 0 siblings, 0 replies; 6+ messages in thread From: Wanpeng Li @ 2020-01-13 1:32 UTC (permalink / raw) To: Thomas Gleixner Cc: LKML, Ingo Molnar, Peter Zijlstra, Ingo Molnar, kvm, Frederic Weisbecker On Fri, 10 Jan 2020 at 22:12, Thomas Gleixner <tglx@linutronix.de> wrote: > > Wanpeng, > > Wanpeng Li <kernellwp@gmail.com> writes: > > > Hi Thomas, > > On Wed, 23 Oct 2019 at 16:29, Thomas Gleixner <tglx@linutronix.de> wrote: > >> > >> On Wed, 23 Oct 2019, Wanpeng Li wrote: > >> > I didn't see your refactor to get_nohz_timer_target() which you > >> > mentioned in IRC after four months, I can observe cyclictest drop from > >> > 4~5us to 8us in kvm guest(we offload the lapic timer emulation to > >> > housekeeping cpu to avoid timer fire external interrupt on the pCPU > >> > which vCPU resident incur a vCPU vmexit) w/o this patch in the case of > >> > there is no busy housekeeping cpu. The score can be recovered after I > >> > give stress to create a busy housekeeping cpu. > >> > > >> > Could you consider applying this patch for temporary since I'm not > >> > sure when the refactor can be ready. > >> > >> Yeah. It's delayed (again).... Will pick that up. > > > > I didn't find WIP tag for this work after ~half year since v4 was > > posted https://lkml.org/lkml/2019/6/28/231 Could you apply this patch > > for temporary because the completion time of refactor is not > > deterministic. > > Could you please repost it? Just repost, thanks Thomas. Wanpeng ^ permalink raw reply [flat|nested] 6+ messages in thread
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2019-10-23 8:16 ` [PATCH v2] sched/nohz: Optimize get_nohz_timer_target() Wanpeng Li
2019-10-23 8:29 ` Thomas Gleixner
2019-10-23 9:25 ` Wanpeng Li
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2020-01-13 1:32 ` Wanpeng Li
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