From: Paolo Bonzini <pbonzini@redhat.com>
To: Fam Zheng <famz@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
xigao@redhat.com, qemu-devel@nongnu.org,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction
Date: Thu, 08 Jan 2015 14:00:04 +0100 [thread overview]
Message-ID: <54AE7F54.1090907@redhat.com> (raw)
In-Reply-To: <20150108025346.GB3221@fam-t430.nay.redhat.com>
On 08/01/2015 03:53, Fam Zheng wrote:
>>> > > 1) Remove 1ns PR_SET_TIMERSLACK in timerfd+epoll, this doesn't make qemu_poll
>>> > > faster than the old qemu_poll_ns, but may have other positive effects that
>>> > > compensate the cost.
>> >
>> > Sounds like a random hack. What is the reasoning for messing with timer
>> > slack?
> In a test this doesn't work. The reason is that timer slack affects poll
> sys calls' timeout, therefore they are correlated. Anyway, I've left this.
1ns is definitely too much, it's just accuracy theater (and I am
responsible for it). We don't care about 3 clock cycles when a context
switch is at least 500.
We probably could change it to 100 ns (0.1 us) with no practical
effects; the default is 50 us.
Paolo
prev parent reply other threads:[~2015-01-08 13:00 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-12-04 3:43 [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 1/6] poll: Introduce QEMU Poll API Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 2/6] posix-aio: Use QEMU poll interface Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 3/6] poll: Add epoll implementation for qemu_poll Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 4/6] main-loop: Replace qemu_poll_ns with qemu_poll Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 5/6] tests: Add test case for qemu_poll Fam Zheng
2014-12-04 3:43 ` [Qemu-devel] [PATCH v2 6/6] poll-linux: Add timerfd support Fam Zheng
2014-12-16 2:04 ` [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction Fam Zheng
2015-01-07 15:08 ` Stefan Hajnoczi
2015-01-08 2:53 ` Fam Zheng
2015-01-08 13:00 ` Paolo Bonzini [this message]
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