From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takuya Yoshikawa Subject: Re: [RFC] sched: make callers check lock contention for cond_resched_lock() Date: Thu, 3 May 2012 22:00:50 +0900 Message-ID: <20120503220050.e91938418f882b4075526e08@gmail.com> References: <20120503171244.2debdd80931ccf35f387c5fe@gmail.com> <1336034127.13683.197.camel@twins> <20120503212244.6abbfa8bc3f46a7f7a932bb7@gmail.com> <1336048150.22523.17.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: mingo@elte.hu, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, avi@redhat.com, mtosatti@redhat.com, yoshikawa.takuya@oss.ntt.co.jp To: Peter Zijlstra Return-path: Received: from mail-pb0-f46.google.com ([209.85.160.46]:49979 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751236Ab2ECNAz (ORCPT ); Thu, 3 May 2012 09:00:55 -0400 In-Reply-To: <1336048150.22523.17.camel@twins> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Thu, 03 May 2012 14:29:10 +0200 Peter Zijlstra wrote: > On Thu, 2012-05-03 at 21:22 +0900, Takuya Yoshikawa wrote: > > Although the real use case is out of this RFC patch, we are now discussing > > a case in which we may hold a spin_lock for long time, ms order, depending > > on workload; and in that case, other threads -- VCPU threads -- should be > > given higher priority for that problematic lock. > > Firstly, if you can hold a lock that long, it shouldn't be a spinlock, I agree with you in principle, but isn't cond_resched_lock() there for that? > secondly why isn't TIF_RESCHED being set if its running that long? That > should still make cond_resched_lock() break. I see. I did some tests using spin_is_contended() and need_resched() and saw that need_resched() was called as often as spin_is_contended(), so experimentally I understand your point. But as I could not see why spin_needbreak() was differently implemented depending on CONFIG_PREEMPT, I wanted to understand the meaning. Thanks, Takuya