From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 106398 invoked by alias); 17 Aug 2016 18:35:42 -0000 Mailing-List: contact systemtap-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Post: List-Help: , Sender: systemtap-owner@sourceware.org Received: (qmail 106317 invoked by uid 89); 17 Aug 2016 18:35:41 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.4 required=5.0 tests=BAYES_00,RP_MATCHES_RCVD,SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=H*i:sk:8af2d58, H*f:sk:8af2d58, H*MI:sk:8af2d58, yours X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with ESMTP; Wed, 17 Aug 2016 18:35:40 +0000 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CCE4F4E4C2; Wed, 17 Aug 2016 18:35:38 +0000 (UTC) Received: from fche.csb (vpn-60-20.rdu2.redhat.com [10.10.60.20]) by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u7HIZcQj014223; Wed, 17 Aug 2016 14:35:38 -0400 Received: by fche.csb (Postfix, from userid 2569) id 885E558C4D; Wed, 17 Aug 2016 14:35:37 -0400 (EDT) Date: Wed, 17 Aug 2016 18:35:00 -0000 From: "Frank Ch. Eigler" To: Avi Kivity Cc: Mark Wielaard , David Smith , systemtap@sourceware.org Subject: Re: Some newbie questions Message-ID: <20160817183537.GB4647@redhat.com> References: <91592a2a-7373-6a27-413c-cf4aca70cb76@scylladb.com> <20160810164742.GF13748@redhat.com> <382185d7-86d6-45d0-1855-d7e3c1639083@scylladb.com> <42a5bad6-c094-cb7a-6f89-a592367ca30b@scylladb.com> <20160811161845.GC12190@redhat.com> <8af2d587-ebc0-730b-3b1c-a452c486af57@scylladb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8af2d587-ebc0-730b-3b1c-a452c486af57@scylladb.com> User-Agent: Mutt/1.4.2.2i X-SW-Source: 2016-q3/txt/msg00171.txt.bz2 Hi - On Wed, Aug 17, 2016 at 09:30:38PM +0300, Avi Kivity wrote: > [...] > >>My load indeed calls epoll_wait() at a high rate, with zero timeout. > >[...] > Yes. It's not very common, but some high throughput or latency > sensitive applications will poll. In my case it's both high throughput > and latency sensitive. Interesting. I assume you've measured that. > [...] > >looks for mmap/exec syscalls. Perhaps there could be a mode (a -D > >setting?) for selecting kprobes rather than syscall-tracepoints to > >catch those events. > > Why not trace just mmap and exec syscalls, rather than everything? > Surely there's a static tracepoint for those. Heh, in this case it's "surely not". :-) There exists only a multiplexed system-call-entry and a system-call-exit pair of tracepoints. > I'd say defaulting to taking a spinlock on every syscall is going to > cause anyone who's using more than a laptop a lot of pain. There may well exist optimization opportunities that would benefit syscall-saturated applications such as yours. - FChE