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[209.85.128.41]) by smtp.gmail.com with ESMTPSA id ku21-20020a170907789500b0072b3464c043sm2036532ejc.116.2022.07.22.07.02.54 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 22 Jul 2022 07:02:55 -0700 (PDT) Received: by mail-wm1-f41.google.com with SMTP id c22so2853341wmr.2 for ; Fri, 22 Jul 2022 07:02:54 -0700 (PDT) X-Received: by 2002:a05:600c:4e86:b0:3a3:2edc:bcb4 with SMTP id f6-20020a05600c4e8600b003a32edcbcb4mr7946235wmq.85.1658498574397; Fri, 22 Jul 2022 07:02:54 -0700 (PDT) MIME-Version: 1.0 References: <20211116012912.723980-1-longman@redhat.com> <20220719104104.1634-1-hdanton@sina.com> <20220722115510.2101-1-hdanton@sina.com> In-Reply-To: <20220722115510.2101-1-hdanton@sina.com> From: Doug Anderson Date: Fri, 22 Jul 2022 07:02:42 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v5] locking/rwsem: Make handoff bit handling more consistent To: Hillf Danton Cc: Waiman Long , Peter Zijlstra , Will Deacon , Davidlohr Bueso , MM , LKML Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658498581; a=rsa-sha256; cv=none; b=L5/ACGPsv1AGFMszccPI439WSqoloDep18cwJDA2Q95FSzEvQJI99C4sUBdnhoWDqKaFuz G6b9E6x66kZySEfIXzQW+Zj8/8pqc1KKYvg8gQF8DtWwG1sWeyl+c3hC7JZdFIuuas956s WKYjp1W0nXoT7sgKF4CWHJTsdTX05TA= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=ZhaNdgdZ; spf=pass (imf28.hostedemail.com: domain of dianders@chromium.org designates 209.85.218.48 as permitted sender) smtp.mailfrom=dianders@chromium.org; dmarc=pass (policy=none) header.from=chromium.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658498581; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=u8dhudGEc/vsjtMExBcnd/syEyEJ59zKIhFV3K8lnhE=; b=wGYvAk1v7rKikUrSzheTH7+/XHh92utzOhbXZEUactB636nSMSUnkZ8OFudoZxXlJt97BE HWEOEzodAaY1T/1zMTwo1V05cK6DSco6NGi65SzglsmozGBYJPd5IuLVDp3E3NDKDW0jnp Cu5Nj3NlmhUeTkH/ge6au8OQ2TnGGfo= Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=chromium.org header.s=google header.b=ZhaNdgdZ; spf=pass (imf28.hostedemail.com: domain of dianders@chromium.org designates 209.85.218.48 as permitted sender) smtp.mailfrom=dianders@chromium.org; dmarc=pass (policy=none) header.from=chromium.org X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 03D26C00A7 X-Stat-Signature: kjsyxgj15n7tssbaighdcp5esd3fjyk6 X-Rspam-User: X-HE-Tag: 1658498580-89342 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi, On Fri, Jul 22, 2022 at 4:55 AM Hillf Danton wrote: > > On Tue, 19 Jul 2022 08:30:02 -0700 Doug Anderson wrote: > > > > I haven't done any stress testing other than my test case, though, so > > I can't speak to whether there might be any other unintended issues. > > The diff below is prepared for any regressions I can imagine in stress > tests by adding changes to both read and write acquirer slow pathes. > > On the read side, make lock stealing more aggressive; on the other hand, > write acquirers try to set HANDOFF after a RWSEM_WAIT_TIMEOUT nap to > force the reader acquirers to take the slow path. > > Hillf > > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -992,13 +992,7 @@ rwsem_down_read_slowpath(struct rw_semap > struct rwsem_waiter waiter; > DEFINE_WAKE_Q(wake_q); > > - /* > - * To prevent a constant stream of readers from starving a sleeping > - * waiter, don't attempt optimistic lock stealing if the lock is > - * currently owned by readers. > - */ > - if ((atomic_long_read(&sem->owner) & RWSEM_READER_OWNED) && > - (rcnt > 1) && !(count & RWSEM_WRITER_LOCKED)) > + if (WARN_ON_ONCE(count & RWSEM_FLAG_READFAIL)) > goto queue; > > /* > @@ -1169,7 +1163,11 @@ rwsem_down_write_slowpath(struct rw_sema > goto trylock_again; > } > > - schedule(); > + if (RWSEM_FLAG_HANDOFF & atomic_long_read(&sem->count)) > + schedule(); > + else > + schedule_timeout(1 + RWSEM_WAIT_TIMEOUT); > + > lockevent_inc(rwsem_sleep_writer); > set_current_state(state); > trylock_again: > -- Thanks! I added this diff to your previous diff and my simple test still passes and I don't see your WARN_ON triggered. How do we move forward? Are you going to officially submit a patch with both of your diffs squashed together? Are we waiting for additional review from someone? -Doug