From: Rodrigo Vivi <rodrigo.vivi@intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915/selftests: Provide full mb() around clflush
Date: Fri, 6 Jul 2018 13:31:56 -0700 [thread overview]
Message-ID: <20180706203156.GD23473@intel.com> (raw)
In-Reply-To: <153090886221.7594.9469545348039815576@cwilso3-mobl.ger.corp.intel.com>
On Fri, Jul 06, 2018 at 09:27:47PM +0100, Chris Wilson wrote:
> Quoting Rodrigo Vivi (2018-07-06 21:23:00)
> > On Fri, Jul 06, 2018 at 06:49:26PM +0100, Chris Wilson wrote:
> > > clflush is an unserialised instruction and the IA manual strongly advises
> > > you to serialise it with a mb. To be cautious, apply one before and one
> > > after,
> >
> > my understanding is that we need one before and one after anyways,
> > not just a matter of being cautious for being cautious..
> >
> > Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
>
> If you are really careful, you can reduce it to a mb between writes and
> the clflush; and vice verse, the mb between clflush and subsequent
> reads. It's all about prevent the clflush from overtaking or being
> overtaken by the operations it is meant to flush or invalidate
> respectively.
>
> But since we're being paranoid here, do both.
hm... makes sense... better to be paranoid...
> -Chris
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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next prev parent reply other threads:[~2018-07-06 20:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-06 17:49 [PATCH] drm/i915/selftests: Provide full mb() around clflush Chris Wilson
2018-07-06 17:56 ` ✗ Fi.CI.CHECKPATCH: warning for " Patchwork
2018-07-06 18:14 ` ✓ Fi.CI.BAT: success " Patchwork
2018-07-06 20:23 ` [PATCH] " Rodrigo Vivi
2018-07-06 20:27 ` Chris Wilson
2018-07-06 20:31 ` Rodrigo Vivi [this message]
2018-07-07 18:32 ` ✓ Fi.CI.IGT: success for " Patchwork
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