linux-kernel - Re: [PATCH 13/14] staging: android: ion: Do not sync CPU cache on map/unmap

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Date:   Thu, 17 Jan 2019 01:02:43 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     "Andrew F. Davis" <afd@...com>
Cc:     Laura Abbott <labbott@...hat.com>,
        Liam Mark <lmark@...eaurora.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 13/14] staging: android: ion: Do not sync CPU cache on
 map/unmap

On Wed, Jan 16, 2019 at 10:17:23AM -0600, Andrew F. Davis wrote:
> I wouldn't go as far as to remove them just yet.. Liam seems pretty
> adamant that they have valid uses. I'm just not sure performance is one
> of them, maybe in the case of software locks between devices or
> something where there needs to be a lot of back and forth interleaved
> access on small amounts of data?

We shouldn't add unused features to start with.  If mainline users for
them appear we can always add them back once we've reviewed the uses
cases and agree that they are sane and have no better solution.