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Date: Fri, 13 Mar 2015 15:56:33 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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To: Jason Baron <jbaron@akamai.com>, Fam Zheng <famz@redhat.com>
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Subject: Re: [PATCH v4 0/9] epoll: Introduce new syscalls, epoll_ctl_batch
 and epoll_pwait1
References: <1425952155-27603-1-git-send-email-famz@redhat.com> <5501AA6B.2020209@akamai.com> <20150313113122.GA7427@ad.nay.redhat.com> <5502F857.6050505@akamai.com>
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On 13/03/2015 15:46, Jason Baron wrote:
> > The throttling algorithm computes a duration for the next IO, which is used to
> > arm a timer in order to delay the request a bit. As timers are always rounded
> > *UP* to the effective granularity, the timeout being 1ms in epoll_pwait is just
> > too coarse and will lead to severe inaccuracy. With epoll_pwait1, we can avoid
> > the rounding-up.
> 
> right, but we could use the timerfd here to get the desired precision.

Fam, didn't you see slowdowns with few file descriptors
epoll_ctl+epoll_wait+timerfd compared to ppoll?

Do they disappear or improve with epoll_ctl_batch and epoll_pwait1?

Paolo