From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55977) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1tXg-0002mM-My for qemu-devel@nongnu.org; Wed, 24 Jul 2013 03:31:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V1tXf-0007Df-Ql for qemu-devel@nongnu.org; Wed, 24 Jul 2013 03:31:24 -0400 Received: from mail.avalus.com ([2001:41c8:10:1dd::10]:51849) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1tXf-0007DV-L6 for qemu-devel@nongnu.org; Wed, 24 Jul 2013 03:31:23 -0400 Date: Wed, 24 Jul 2013 08:31:07 +0100 From: Alex Bligh Message-ID: <11E9299201E9A8D837D212DB@nimrod.local> In-Reply-To: <51EF7752.9020505@redhat.com> References: <1374396185-10870-1-git-send-email-pingfank@linux.vnet.ibm.com> <429B80A9A0DBF7FBF05E7C5A@nimrod.local> <628DFBF37B094813C72B6DBF@Ximines.local> <51EE5B34.10507@redhat.com> <51EF7752.9020505@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Content-Disposition: inline Subject: Re: [Qemu-devel] [RFC 0/8] arm AioContext with its own timer stuff Reply-To: Alex Bligh List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , liu ping fan Cc: Kevin Wolf , Alex Bligh , Jan Kiszka , Stefan Hajnoczi , qemu-devel@nongnu.org, Anthony Liguori --On 24 July 2013 08:42:26 +0200 Paolo Bonzini wrote: > With ppoll, is this true or just hearsay? > > (Without ppoll, indeed setitimer has 1 us resolution while poll has 1 > ms; too bad that select has other problems, because select has also 1 us > resolution). Most 'reasonable' POSIX compliant operating systems have ppoll and I would have thought there is /better/ resolution there than relying not only on signal, but also a pipe or eventfd plus the underlying poll(). If it was my comments you are referring to, my concern was mainly about Windows (which I know very little about), as there does not appear to be a nanosecond or even microsecond alternative to WaitForMultipleObjects. However, articles like this: http://social.msdn.microsoft.com/Forums/vstudio/en-US/e8a7cb1e-9edd-4ee3-982e-f66b7bf6ae44/improve-accuracy-waitforsingleobject suggest that WaitFor{Single,Multiple}Objects can have pretty appalling latency anyway (100ms!), and there's no evidence that's limited by making one of the FDs (or objects) ready. In these circumstances, I'd question whether we gain anything by worrying about timer resolution. -- Alex Bligh