2017-11-13 18:53 GMT+08:00 Juergen Gross <jgross@xxxxxxxx>: > On 13/11/17 11:06, Quan Xu wrote: >> From: Quan Xu <quan.xu0@xxxxxxxxx> >> >> 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@xxxxxxxxx> >> Signed-off-by: Quan Xu <quan.xu0@xxxxxxxxx> >> Cc: Juergen Gross <jgross@xxxxxxxx> >> Cc: Alok Kataria <akataria@xxxxxxxxxx> >> Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx> >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> >> Cc: Ingo Molnar <mingo@xxxxxxxxxx> >> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> >> Cc: x86@xxxxxxxxxx >> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx >> Cc: linux-kernel@xxxxxxxxxxxxxxx >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx > > 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
