From patchwork Tue Jun 14 08:11:25 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Joonsoo Kim X-Patchwork-Id: 9175167 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 6032A6048C for ; Tue, 14 Jun 2016 08:11:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 50C4D21327 for ; Tue, 14 Jun 2016 08:11:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 455B92804C; Tue, 14 Jun 2016 08:11:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 3917721327 for ; Tue, 14 Jun 2016 08:11:35 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1bCjQ2-00051o-Kb; Tue, 14 Jun 2016 08:09:54 +0000 Received: from lgeamrelo11.lge.com ([156.147.23.51]) by bombadil.infradead.org with esmtp (Exim 4.80.1 #2 (Red Hat Linux)) id 1bCjPx-0004yd-Pt for linux-arm-kernel@lists.infradead.org; Tue, 14 Jun 2016 08:09:51 +0000 Received: from unknown (HELO lgeamrelo02.lge.com) (156.147.1.126) by 156.147.23.51 with ESMTP; 14 Jun 2016 17:09:26 +0900 X-Original-SENDERIP: 156.147.1.126 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Received: from unknown (HELO localhost) (10.177.222.138) by 156.147.1.126 with ESMTP; 14 Jun 2016 17:09:20 +0900 X-Original-SENDERIP: 10.177.222.138 X-Original-MAILFROM: iamjoonsoo.kim@lge.com Date: Tue, 14 Jun 2016 17:11:25 +0900 From: Joonsoo Kim To: Geert Uytterhoeven Subject: Re: Boot failure on emev2/kzm9d (was: Re: [PATCH v2 11/11] mm/slab: lockless decision to grow cache) Message-ID: <20160614081125.GA17700@js1304-P5Q-DELUXE> References: <20160614062456.GB13753@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20160614_010950_182790_BFFB0158 X-CRM114-Status: GOOD ( 25.80 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-renesas-soc@vger.kernel.org, David Rientjes , "linux-kernel@vger.kernel.org" , Pekka Enberg , Linux MM , Jesper Dangaard Brouer , Andrew Morton , Christoph Lameter , "linux-arm-kernel@lists.infradead.org" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP On Tue, Jun 14, 2016 at 09:31:23AM +0200, Geert Uytterhoeven wrote: > Hi Joonsoo, > > On Tue, Jun 14, 2016 at 8:24 AM, Joonsoo Kim wrote: > > On Mon, Jun 13, 2016 at 09:43:13PM +0200, Geert Uytterhoeven wrote: > >> On Tue, Apr 12, 2016 at 6:51 AM, wrote: > >> > From: Joonsoo Kim > >> > To check whther free objects exist or not precisely, we need to grab a > >> > lock. But, accuracy isn't that important because race window would be > >> > even small and if there is too much free object, cache reaper would reap > >> > it. So, this patch makes the check for free object exisistence not to > >> > hold a lock. This will reduce lock contention in heavily allocation case. > >> > > >> > Note that until now, n->shared can be freed during the processing by > >> > writing slabinfo, but, with some trick in this patch, we can access it > >> > freely within interrupt disabled period. > >> > > >> > Below is the result of concurrent allocation/free in slab allocation > >> > benchmark made by Christoph a long time ago. I make the output simpler. > >> > The number shows cycle count during alloc/free respectively so less is > >> > better. > >> > > >> > * Before > >> > Kmalloc N*alloc N*free(32): Average=248/966 > >> > Kmalloc N*alloc N*free(64): Average=261/949 > >> > Kmalloc N*alloc N*free(128): Average=314/1016 > >> > Kmalloc N*alloc N*free(256): Average=741/1061 > >> > Kmalloc N*alloc N*free(512): Average=1246/1152 > >> > Kmalloc N*alloc N*free(1024): Average=2437/1259 > >> > Kmalloc N*alloc N*free(2048): Average=4980/1800 > >> > Kmalloc N*alloc N*free(4096): Average=9000/2078 > >> > > >> > * After > >> > Kmalloc N*alloc N*free(32): Average=344/792 > >> > Kmalloc N*alloc N*free(64): Average=347/882 > >> > Kmalloc N*alloc N*free(128): Average=390/959 > >> > Kmalloc N*alloc N*free(256): Average=393/1067 > >> > Kmalloc N*alloc N*free(512): Average=683/1229 > >> > Kmalloc N*alloc N*free(1024): Average=1295/1325 > >> > Kmalloc N*alloc N*free(2048): Average=2513/1664 > >> > Kmalloc N*alloc N*free(4096): Average=4742/2172 > >> > > >> > It shows that allocation performance decreases for the object size up to > >> > 128 and it may be due to extra checks in cache_alloc_refill(). But, with > >> > considering improvement of free performance, net result looks the same. > >> > Result for other size class looks very promising, roughly, 50% performance > >> > improvement. > >> > > >> > v2: replace kick_all_cpus_sync() with synchronize_sched(). > >> > > >> > Signed-off-by: Joonsoo Kim > >> > >> I've bisected a boot failure (no output at all) in v4.7-rc2 on emev2/kzm9d > >> (Renesas dual Cortex A9) to this patch, which is upstream commit > >> 801faf0db8947e01877920e848a4d338dd7a99e7. > >> > >> I've attached my .config. I don't know if it also happens with > >> shmobile_defconfig, as something went wrong with my remote access to the board, > >> preventing further testing. I also couldn't verify if the issue persists in > >> v4.7-rc3. > > In the mean time, I've verified it also happens with shmobile_defconfig. > > >> > >> Do you have a clue? > > > > I don't have yet. Could you help me to narrow down the problem? > > Following diff is half-revert change to check that synchronize_sched() > > has no problem. > > Thanks! > > Unfortunately the half revert is not sufficient. The full revert is. Thanks for quick testing! Could I ask one more time to check that synchronize_sched() is root cause of the problem? Testing following two diffs will be helpful to me. Thanks. ------->8-------- diff --git a/mm/slab.c b/mm/slab.c index 763096a..d892364 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -965,7 +965,7 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * freed after synchronize_sched(). */ if (force_change) - synchronize_sched(); + kick_all_cpus_sync(); fail: kfree(old_shared); ------->8------ diff --git a/mm/slab.c b/mm/slab.c index 763096a..38d99c2 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -964,8 +964,6 @@ static int setup_kmem_cache_node(struct kmem_cache *cachep, * guaranteed to be valid until irq is re-enabled, because it will be * freed after synchronize_sched(). */ - if (force_change) - synchronize_sched(); fail: kfree(old_shared);