From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f197.google.com (mail-wr0-f197.google.com [209.85.128.197]) by kanga.kvack.org (Postfix) with ESMTP id E13052806EA for ; Thu, 20 Apr 2017 09:25:40 -0400 (EDT) Received: by mail-wr0-f197.google.com with SMTP id k14so5621668wrc.16 for ; Thu, 20 Apr 2017 06:25:40 -0700 (PDT) Received: from mail-wm0-x244.google.com (mail-wm0-x244.google.com. [2a00:1450:400c:c09::244]) by mx.google.com with ESMTPS id g55si9051279wra.249.2017.04.20.06.25.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 20 Apr 2017 06:25:39 -0700 (PDT) Received: by mail-wm0-x244.google.com with SMTP id u65so3108421wmu.3 for ; Thu, 20 Apr 2017 06:25:39 -0700 (PDT) Date: Thu, 20 Apr 2017 15:25:37 +0200 From: Frederic Weisbecker Subject: Re: Heads-up: two regressions in v4.11-rc series Message-ID: <20170420132536.GB25160@lerouge> References: <20170420110042.73d01e0f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170420110042.73d01e0f@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jesper Dangaard Brouer Cc: Linus Torvalds , Andrew Morton , Mel Gorman , Tariq Toukan , LKML , linux-mm , "netdev@vger.kernel.org" , peterz@infradead.org On Thu, Apr 20, 2017 at 11:00:42AM +0200, Jesper Dangaard Brouer wrote: > Hi Linus, > > Just wanted to give a heads-up on two regressions in 4.11-rc series. > > (1) page allocator optimization revert > > Mel Gorman and I have been playing with optimizing the page allocator, > but Tariq spotted that we caused a regression for (NIC) drivers that > refill DMA RX rings in softirq context. > > The end result was a revert, and this is waiting in AKPMs quilt queue: > http://ozlabs.org/~akpm/mmots/broken-out/revert-mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch > > > (2) Busy softirq can cause userspace not to be scheduled > > I bisected the problem to a499a5a14dbd ("sched/cputime: Increment > kcpustat directly on irqtime account"). See email thread with > Subject: Bisected softirq accounting issue in v4.11-rc1~170^2~28 > http://lkml.kernel.org/r/20170328101403.34a82fbf@redhat.com > > I don't know the scheduler code well enough to fix this, and will have > to rely others to figure out this scheduler regression. > > To make it clear: I'm only seeing this scheduler regression when a > remote host is sending many many network packets, towards the kernel > which keeps NAPI/softirq busy all the time. A possible hint: tool > "top" only shows this in "si" column, while on v4.10 "top" also blames > "ksoftirqd/N", plus "ps" reported cputime (0:00) seems wrong for ksoftirqd. (I'm currently working on reproducing that one.) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org