[Qemu-devel] Re: [RFC] Some more io-thread optimizations

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-02-15 23:03, Marcelo Tosatti wrote:
> On Mon, Feb 14, 2011 at 10:50:42AM +0100, Jan Kiszka wrote:
>> Hi,
>>
>> patch below further reduces the io-thread overhead in tcg mode so that
>> specifically emulating smp boxes gets noticeably faster. Its essence:
>> poll the file descriptors until select returns 0, keeping the global
>> mutex locked. This reduces ping pong with the vcpu threads, most
>> noticeably in tcg mode where we run in lock-step.
>>
>> Split up in two patches, I'm planning to route those changes via the kvm
>> queue (as they collide with other patches there).
>>
>> Jan
> 
> Not sure this makes sense for all cases. There could be scenarios where
> a single pass is more efficient (think latency to acquire mutex from
> vcpu context in kvm mode, with intensive file IO in progress).

Yeah, likely true. Only TCG has these insane long lock-holding times and
requires signal-based mutex handover. I will exclude KVM from this.

Jan


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