Re: [PATCH v5 07/13] block: Add PCI P2P flag for request queue and check support for requests
On 9/3/18 4:26 PM, Logan Gunthorpe wrote:
On 01/09/18 02:28 AM, Christoph Hellwig wrote:
> On Thu, Aug 30, 2018 at 01:11:18PM -0600, Jens Axboe wrote:
>> I think this belongs in the caller - both the validity check, and
>> passing in NOMERGE for this type of request. I don't want to impose
>> this overhead on everything, for a pretty niche case.
>
> It is just a single branch, which will be predicted as not taken
> for non-P2P users. The benefit is that we get proper error checking
> by doing it in the block code.
I personally agree with Christoph. But if there's consensus in the other
direction or this is a real blocker moving this forward, I can remove it
for the next version.
It's a simple branch because the check isn't exhaustive. It just checks
the first page. At that point you may as well just require the caller to
flag the bio/rq as being P2P, and then do a check for P2P compatibility
with the queue.
--
Jens Axboe