Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758280AbZFQT41 (ORCPT ); Wed, 17 Jun 2009 15:56:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753338AbZFQT4S (ORCPT ); Wed, 17 Jun 2009 15:56:18 -0400 Received: from x35.xmailserver.org ([64.71.152.41]:44715 "EHLO x35.xmailserver.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753180AbZFQT4R (ORCPT ); Wed, 17 Jun 2009 15:56:17 -0400 X-AuthUser: davidel@xmailserver.org Date: Wed, 17 Jun 2009 12:50:10 -0700 (PDT) From: Davide Libenzi X-X-Sender: davide@makko.or.mcafeemobile.com To: Gregory Haskins cc: "Michael S. Tsirkin" , kvm@vger.kernel.org, Linux Kernel Mailing List , avi@redhat.com, paulmck@linux.vnet.ibm.com, Ingo Molnar Subject: Re: [KVM-RFC PATCH 1/2] eventfd: add an explicit srcu based notifier interface In-Reply-To: <4A39415C.9060803@novell.com> Message-ID: References: <20090616022041.23890.90120.stgit@dev.haskins.net> <20090616022956.23890.63776.stgit@dev.haskins.net> <20090616140240.GA9401@redhat.com> <4A37A7FC.4090403@novell.com> <20090616143816.GA18196@redhat.com> <4A37B0BB.3020005@novell.com> <20090616145502.GA1102@redhat.com> <4A37B832.6040206@novell.com> <20090616154150.GA17494@redhat.com> <4A37C592.2030407@novell.com> <4A37CFDA.4000602@novell.com> <4A3927C0.5060607@novell.com> <4A39415C.9060803@novell.com> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) X-GPG-FINGRPRINT: CFAE 5BEE FD36 F65E E640 56FE 0974 BF23 270F 474E X-GPG-PUBLIC_KEY: http://www.xmailserver.org/davidel.asc MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1265 Lines: 36 On Wed, 17 Jun 2009, Gregory Haskins wrote: > Davide Libenzi wrote: > > > How much the (possible, but not certain) kernel thread context switch time > > weighs in the overall KVM IRQ service time? > > > > Generally each one is costing me about 7us on average. For something > like high-speed networking, we have a path that has about 30us of > base-line overhead. So one additional ctx-switch puts me at base+7 ( = > ~37us), two puts me in base+2*7 (= ~44us). So in that context (no pun > intended ;), it hurts quite a bit. I'll be the first to admit that not > everyone (most?) will care about latency, though. But FWIW, I do. And how a frame reception is handled in Linux nowadays? > True, but thats the notifiee's burden, not eventfd's. And its always > going to be opt-in. Even today, someone is free to either try to sleep > (which will oops on the might_sleep()), ... No, today you just can't sleep. As you can't sleep in any callback-registered wakeups, like epoll, for example. - Davide -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/