Messages in this thread | | | From | Wanpeng Li <> | Date | Mon, 13 Nov 2017 19:09:09 +0800 | Subject | Re: [PATCH RFC v3 1/6] x86/paravirt: Add pv_idle_ops to paravirt ops |
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2017-11-13 18:53 GMT+08:00 Juergen Gross <jgross@suse.com>: > 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? 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.
There is a "Adaptive halt-polling" which are merged to upstream more than two years ago avoids to thread the critical path and has already been ported to other architectures. https://lkml.org/lkml/2015/9/3/615
Regards, Wanpeng Li
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