linux-kernel - Re: [Intel-wired-lan] [net-next PATCH 25/27] igb: Update driver to make use of DMA_ATTR_SKIP_CPU

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Message-ID: <1477502465.2431.0.camel@intel.com>
Date:   Wed, 26 Oct 2016 10:21:05 -0700
From:   Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:     Alexander Duyck <alexander.h.duyck@...el.com>,
        netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     davem@...emloft.net, brouer@...hat.com
Subject: Re: [Intel-wired-lan] [net-next PATCH 25/27] igb: Update driver to
 make use of DMA_ATTR_SKIP_CPU_SYNC

On Tue, 2016-10-25 at 11:39 -0400, Alexander Duyck wrote:
> The ARM architecture provides a mechanism for deferring cache line
> invalidation in the case of map/unmap.  This patch makes use of this
> mechanism to avoid unnecessary synchronization.
> 
> A secondary effect of this change is that the portion of the page that
> has
> been synchronized for use by the CPU should be writable and could be
> passed
> up the stack (at least on ARM).
> 
> The last bit that occurred to me is that on architectures where the
> sync_for_cpu call invalidates cache lines we were prefetching and then
> invalidating the first 128 bytes of the packet.  To avoid that I have
> moved
> the sync up to before we perform the prefetch and allocate the skbuff so
> that we can actually make use of it.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> 

Acked-by: Jeff Kirsher <jeffrey.t.kirsher@...el.com>
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