Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758804Ab0FPPQ6 (ORCPT ); Wed, 16 Jun 2010 11:16:58 -0400 Received: from mail.gmx.net ([213.165.64.20]:40349 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754954Ab0FPPQ5 (ORCPT ); Wed, 16 Jun 2010 11:16:57 -0400 X-Authenticated: #14349625 X-Provags-ID: V01U2FsdGVkX1/uR449MuHu8/8Xze2BR2Qlfg4l0Ogc9T2duw8x/B Y6mVn7XnZSxabG Subject: Re: Slow pty's (was Re: libdivecomputer interfaces?) From: Mike Galbraith To: Jiri Kosina Cc: Brian Bloniarz , Chris Wedgwood , Linus Torvalds , Greg KH , Alan Cox , OGAWA Hirofumi , Jef Driesen , linux-kernel@vger.kernel.org In-Reply-To: References: <20100610181042.GA19210@puku.stupidest.org> <4C116652.8010408@athenacr.com> Content-Type: text/plain Date: Wed, 16 Jun 2010 17:16:51 +0200 Message-Id: <1276701411.30669.6.camel@marge.simson.net> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1.1 Content-Transfer-Encoding: 7bit X-Y-GMX-Trusted: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1931 Lines: 54 On Wed, 2010-06-16 at 17:03 +0200, Jiri Kosina wrote: > On Thu, 10 Jun 2010, Brian Bloniarz wrote: > > > On 06/10/2010 02:10 PM, Chris Wedgwood wrote: > > > (sorry if this reponse isn't on target, i was just pointed to this > > > thread a few minutes ago) > > > > > > > > > On Thu, Jun 10, 2010 at 10:25:36AM -0700, Linus Torvalds wrote: > > > > > >> I thought we long since (ie back last fall) fixed the latency > > >> problems with pty's, but there does seem to be something very fishy > > >> going on there still. > > > > > > this might not be related, but i have slow serial ports with NOHZ that > > > goes away when i revert 39c0cbe2150cbd848a25ba6cdb271d1ad46818ad. > > > > Unrelated or not, I think Chris is right about this. Somewhere before > > -rc1, the emulated serial console on my KVM instance became slow > > to echo input. I just tested with the commit reverted and it's > > back to normal. > > So let's CC Mike then. Chris already gave me a heads up, it's on my todo. The old P4 box I use for a serial console box is exploding on boot, or I would have already had a look. > > > and looking at the only two interesting hunks it's not clear why: Complete mystery to me. > > > +int nohz_ratelimit(int cpu) > > > +{ > > > + struct rq *rq = cpu_rq(cpu); > > > + u64 diff = rq->clock - rq->nohz_stamp; > > > + > > > + rq->nohz_stamp = rq->clock; > > > + > > > + return diff < (NSEC_PER_SEC / HZ) >> 1; > > > +} > > > > > > + if (nohz_ratelimit(cpu)) > > > + goto end; > > > + > > > > > > network latnecy is fine, and if i create lots of wakeups (network IO > > > is fine) then the serial port latency is noticable -- 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/