Messages in this thread | | | Subject | Re: [LKP] [mm] 9bc8039e71: will-it-scale.per_thread_ops -64.1% regression | From | kemi <> | Date | Fri, 28 Dec 2018 10:55:05 +0800 |
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On 2018/12/28 上午10:55, Waiman Long wrote: > On 12/27/2018 08:31 PM, Wang, Kemi wrote: >> Hi, Waiman >> Did you post that patch? Let's see if it helps. > > I did post the patch a while ago. I will need to rebase it to a new > baseline. Will do that in a week or 2. >
OK.I will take a look at it and try to rebase it on shi's patch to see if the regression can be fixed. May I know where I can get that patch, I didn't find it in my inbox. Thanks
> -Longman > >> >> -----Original Message----- >> From: LKP [mailto:lkp-bounces@lists.01.org] On Behalf Of Waiman Long >> Sent: Tuesday, November 6, 2018 6:40 AM >> To: Linus Torvalds <torvalds@linux-foundation.org>; vbabka@suse.cz; Davidlohr Bueso <dave@stgolabs.net> >> Cc: yang.shi@linux.alibaba.com; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; Matthew Wilcox <willy@infradead.org>; mhocko@kernel.org; Colin King <colin.king@canonical.com>; Andrew Morton <akpm@linux-foundation.org>; ldufour@linux.vnet.ibm.com; lkp@01.org; kirill.shutemov@linux.intel.com >> Subject: Re: [LKP] [mm] 9bc8039e71: will-it-scale.per_thread_ops -64.1% regression >> >> On 11/05/2018 05:14 PM, Linus Torvalds wrote: >>> On Mon, Nov 5, 2018 at 12:12 PM Vlastimil Babka <vbabka@suse.cz> wrote: >>>> I didn't spot an obvious mistake in the patch itself, so it looks >>>> like some bad interaction between scheduler and the mmap downgrade? >>> I'm thinking it's RWSEM_SPIN_ON_OWNER that ends up being confused by >>> the downgrade. >>> >>> It looks like the benchmark used to be basically CPU-bound, at about >>> 800% CPU, and now it's somewhere in the 200% CPU region: >>> >>> will-it-scale.time.percent_of_cpu_this_job_got >>> >>> 800 +-+-------------------------------------------------------------------+ >>> |.+.+.+.+.+.+.+. .+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+.+..+.+.+.+. .+.+.+.| >>> 700 +-+ +. + | >>> | | >>> 600 +-+ | >>> | | >>> 500 +-+ | >>> | | >>> 400 +-+ | >>> | | >>> 300 +-+ | >>> | | >>> 200 O-O O O O O O | >>> | O O O O O O O O O O O O O O O O O O | >>> 100 +-+-------------------------------------------------------------------+ >>> >>> which sounds like the downgrade really messes with the "spin waiting >>> for lock" logic. >>> >>> I'm thinking it's the "wake up waiter" logic that has some bad >>> interaction with spinning, and breaks that whole optimization. >>> >>> Adding Waiman and Davidlohr to the participants, because they seem to >>> be the obvious experts in this area. >>> >>> Linus >> Optimistic spinning on rwsem is done only on writers spinning on a >> writer-owned rwsem. If a write-lock is downgraded to a read-lock, all >> the spinning waiters will quit. That may explain the drop in cpu >> utilization. I do have a old patch that enable a certain amount of >> reader spinning which may help the situation. I can rebase that and send >> it out for review if people have interest. >> >> Cheers, >> Longman >> >> >> _______________________________________________ >> LKP mailing list >> LKP@lists.01.org >> https://lists.01.org/mailman/listinfo/lkp > >
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