[Intel-gfx] [PATCH 3/9] drm/i915/cmdparser: Use cached vmappings

[Matthew Auld]

On 16 August 2016 at 20:10, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Tue, Aug 16, 2016 at 08:04:35PM +0100, Matthew Auld wrote:
>> > +       if (dst_needs_clflush & CLFLUSH_BEFORE)
>> > +               batch_len = roundup(batch_len, boot_cpu_data.x86_clflush_size);
>> hmm, this bit doesn't seem obvious to me. What am I missing?
>
> The code is optimized to work on cachelines (to work on a partial
> cacheline requires a flush before the read). We know that the batch is
> in whole pages and so we can always round up to the end of the next
> cacheline. We also know that we can read more than the declared length
> of the batch into the local page as we only validate as much as
> required. So it is safe to read from beyond the end of the batch, and to
> do so avoids having to insert clflushes before the read.
Ah, right ofc.

Reviewed-by: Matthew Auld <matthew.auld at intel.com>