On 03/08/2017 08:00 AM, Goldwyn Rodrigues wrote:
>
>
> On 03/08/2017 01:03 AM, Sagi Grimberg wrote:
>>
>>> - if (likely(blk_queue_enter(q, false) == 0)) {
>>> + if (likely(blk_queue_enter(q, bio_flagged(bio, BIO_NOWAIT))
>>> == 0)) {
>>> ret = q->make_request_fn(q, bio);
>>
>> I think that for ->make_request to not block we'd need to set
>> BLK_MQ_REQ_NOWAIT in blk_mq_alloc_data to avoid blocking on a tag
>> allocation.
>>
>> Something like the untested addition below:
>
> I did that in the first series, but there are too many reasons to block
> in blk-mq [1]. I dropped blk-mq work in v2.
That's complete nonsense, there are no more places in blk-mq that will
block that in the legacy path. Most of the examples from your URL:
> [1] https://patchwork.kernel.org/patch/9571051/
are not blk-mq, but writeback throttling, and drivers that explicitly
hook into ->make_request_fn.
As others have mentioned, it's a total non-starter to focus on the
deprecated IO path and just ignore the new one. Back to the drawing
board.
--
Jens Axboe
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