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Date:   Tue, 16 Apr 2019 09:50:38 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Waiman Long <longman@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        huang ying <huang.ying.caritas@gmail.com>
Subject: Re: [PATCH v4 10/16] locking/rwsem: Wake up almost all readers in
 wait queue
Message-ID: <20190416165038.xfjserwdhli6p222@linux-r8p5>
References: <20190413172259.2740-1-longman@redhat.com>
 <20190413172259.2740-11-longman@redhat.com>
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On Sat, 13 Apr 2019, Waiman Long wrote:
>+/*
>+ * We limit the maximum number of readers that can be woken up for a
>+ * wake-up call to not penalizing the waking thread for spending too
>+ * much time doing it.
>+ */
>+#define MAX_READERS_WAKEUP	0x100

Although with wake_q this is not really so... Could it at least be
rewritten, dunno something like so:

/*
 * Magic number to batch-wakeup waiting readers, even when writers
 * are also present in the queue. This both limits the amount of
 * work the waking thread must do (albeit wake_q)  and also prevents
 * any potential counter overflow, however unlikely.
 */

I'm still not crazy about this artificial limit for the readers-only
case, but won't argue. I certainly like the reader/writer case.

Thanks,
Davidlohr