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From: =?UTF-8?B?TWFyYy1BbmRyw6kgTHVyZWF1?= <marcandre.lureau@redhat.com>
Date: Wed, 28 Feb 2018 17:00:58 +0100
Message-ID: <CAMxuvaw-v3BagJ6-50sxW24X3c=S-4Xfd5e1Unq8ScNbxKvkSQ@mail.gmail.com>
Subject: Re: [PATCH v15 11/11] RFC: fw_cfg: do DMA read operation
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Sergio Lopez Pascual <slp@redhat.com>, Baoquan He <bhe@redhat.com>,
        "Somlo, Gabriel" <somlo@cmu.edu>, xiaolong.ye@intel.com
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Hi

On Wed, Feb 28, 2018 at 4:48 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Wed, Feb 28, 2018 at 04:41:51PM +0100, Marc-André Lureau wrote:
>> I don't know if it's always safe to enable dma in read_raw(), how
>> could we know? Is there a check we could use to choose one or ther
>> other (and thus avoiding explicit dma/readfn argument)?
>
> I'm not sure - but does it really matter? Is anyone reading large files
> like this in production where speed matters?
> Why even bother with DMA?

The difference is quite significante for not so small files, as shown above.

And if they access the fw_cfg entries at boot time, or when starting
things etc, this may speed things up.