Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu

From	David Miller <davem@davemloft.net>
Newsgroups	linux.kernel
Subject	Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu
Date	2017-07-20 22:00 +0200
Message-ID	<u5pM7-3kJ-21@gated-at.bofh.it> (permalink)
References	<u14wy-6ML-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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From: Vijay Kumar <vijay.ac.kumar@oracle.com>
Date: Sat,  8 Jul 2017 14:23:42 -0600

> cpu_poke is a low latency path to resume the target cpu if suspended
> using cpu_yield. Use cpu poke to resume cpu if supported by hypervisor.
> 
> 	     hackbench results (lower is better):
> Number of		
> Process:		w/o fix		with fix
> 1  			0.012		 0.010
> 10			0.021		 0.019
> 100			0.151		 0.148

So this only works for a cpu which has yielded.

The kernel sends reschedule events to both idle and non-idle cpus.
That's why you have to have that fallback code to still send the
mondo IPI right?

For the case where POKE works, it seems like completely unnecessary
overhead to set the PIL interrupt.  Just disable local cpu interrupts
and call schedule_ipi() directly.

I bet that improves your benchmark even more.

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Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu David Miller <davem@davemloft.net> - 2017-07-20 22:00 +0200
  Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu Vijay Kumar <vijay.ac.kumar@oracle.com> - 2017-07-21 04:50 +0200
    Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu David Miller <davem@davemloft.net> - 2017-07-21 05:00 +0200
      Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu Vijay Kumar <vijay.ac.kumar@oracle.com> - 2017-07-21 05:40 +0200
        Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu David Miller <davem@davemloft.net> - 2017-07-21 05:50 +0200
          Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu Vijay Kumar <vijay.ac.kumar@oracle.com> - 2017-07-21 06:20 +0200

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