From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42430) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9ChK-0004dQ-6B for qemu-devel@nongnu.org; Thu, 08 Jan 2015 08:00:24 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Y9ChE-0008Fq-VU for qemu-devel@nongnu.org; Thu, 08 Jan 2015 08:00:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56043) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Y9ChE-0008FQ-OR for qemu-devel@nongnu.org; Thu, 08 Jan 2015 08:00:16 -0500 Message-ID: <54AE7F54.1090907@redhat.com> Date: Thu, 08 Jan 2015 14:00:04 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1417664590-23707-1-git-send-email-famz@redhat.com> <20141216020438.GA18251@ad.nay.redhat.com> <20150107150808.GE22440@stefanha-thinkpad.redhat.com> <20150108025346.GB3221@fam-t430.nay.redhat.com> In-Reply-To: <20150108025346.GB3221@fam-t430.nay.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 0/6] aio: Support epoll by introducing qemu_poll abstraction List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng , Stefan Hajnoczi Cc: Kevin Wolf , xigao@redhat.com, qemu-devel@nongnu.org, Stefan Hajnoczi 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