From: Chris Wilson <chris@chris-wilson.co.uk>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: __mutex_lock_common() unlikely very likely
Date: Thu, 19 Jan 2017 08:55:07 +0000 [thread overview]
Message-ID: <20170119085507.GA28607@nuc-i3427.alporthouse.com> (raw)
In-Reply-To: <20170118155824.689a9996@gandalf.local.home>
On Wed, Jan 18, 2017 at 03:58:24PM -0500, Steven Rostedt wrote:
> Chris,
>
> My branch tracer flagged the unlikely in __mutex_lock_common() as
> always hit. That's the:
>
> if (use_ww_ctx) {
> [...]
> if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
> return -EALREADY;
> }
>
> This is hit 100% of the time, and its coming from the drm logic:
By design this is an exceptional case. In practice, drm modesetting is a
little slapsidasical when it comes to locking. However, it is the
minority use case, just that on intel, the more prevalent users do not
hit this path - though they will with the ww_mutex refactoring work. ttm
drivers (amdgpu, nouveau etc) will be demonstrating that this is the
unlikely branch.
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
next prev parent reply other threads:[~2017-01-19 8:55 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-18 20:58 Steven Rostedt
2017-01-19 8:55 ` Chris Wilson [this message]
2017-01-19 13:32 ` Steven Rostedt
2017-01-19 13:54 ` [PATCH] mutex: Remove ww_ctx unlikely() from __mutex_lock_common() Steven Rostedt (VMware)
2017-01-19 16:42 ` Peter Zijlstra
2017-01-19 16:50 ` Steven Rostedt
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