Messages in this thread | | | Subject | Re: [PATCH RFC v3 1/6] x86/paravirt: Add pv_idle_ops to paravirt ops | From | Quan Xu <> | Date | Tue, 14 Nov 2017 15:02:41 +0800 |
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On 2017/11/13 18:53, Juergen Gross wrote: > On 13/11/17 11:06, Quan Xu wrote: >> From: Quan Xu <quan.xu0@gmail.com> >> >> So far, pv_idle_ops.poll is the only ops for pv_idle. .poll is called >> in idle path which will poll for a while before we enter the real idle >> state. >> >> In virtualization, idle path includes several heavy operations >> includes timer access(LAPIC timer or TSC deadline timer) which will >> hurt performance especially for latency intensive workload like message >> passing task. The cost is mainly from the vmexit which is a hardware >> context switch between virtual machine and hypervisor. Our solution is >> to poll for a while and do not enter real idle path if we can get the >> schedule event during polling. >> >> Poll may cause the CPU waste so we adopt a smart polling mechanism to >> reduce the useless poll. >> >> Signed-off-by: Yang Zhang <yang.zhang.wz@gmail.com> >> Signed-off-by: Quan Xu <quan.xu0@gmail.com> >> Cc: Juergen Gross <jgross@suse.com> >> Cc: Alok Kataria <akataria@vmware.com> >> Cc: Rusty Russell <rusty@rustcorp.com.au> >> Cc: Thomas Gleixner <tglx@linutronix.de> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: "H. Peter Anvin" <hpa@zytor.com> >> Cc: x86@kernel.org >> Cc: virtualization@lists.linux-foundation.org >> Cc: linux-kernel@vger.kernel.org >> Cc: xen-devel@lists.xenproject.org > Hmm, is the idle entry path really so critical to performance that a new > pvops function is necessary? Juergen, Here is the data we get when running benchmark netperf: 1. w/o patch and disable kvm dynamic poll (halt_poll_ns=0): 29031.6 bit/s -- 76.1 %CPU
2. w/ patch and disable kvm dynamic poll (halt_poll_ns=0): 35787.7 bit/s -- 129.4 %CPU
3. w/ kvm dynamic poll: 35735.6 bit/s -- 200.0 %CPU
4. w/patch and w/ kvm dynamic poll: 42225.3 bit/s -- 198.7 %CPU
5. idle=poll 37081.7 bit/s -- 998.1 %CPU
w/ this patch, we will improve performance by 23%.. even we could improve performance by 45.4%, if we use w/patch and w/ kvm dynamic poll. also the cost of CPU is much lower than 'idle=poll' case..
> Wouldn't a function pointer, maybe guarded > by a static key, be enough? A further advantage would be that this would > work on other architectures, too.
I assume this feature will be ported to other archs.. a new pvops makes code clean and easy to maintain. also I tried to add it into existed pvops, but it doesn't match.
Quan Alibaba Cloud > > Juergen >
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