[PATCH v3 2/2] blk-mq: Add a polling specific stats function

[Stephen Bates]

> Nah, let's just leave it as-is then, even though I don't think it's the
> prettiest thing I've ever seen.

I did look at making the stats buckets in the request_queue struct based on dir and size. Something like:

-       struct blk_rq_stat      poll_stat[2];
+       struct blk_rq_stat      poll_stat[2][BLK_MQ_POLL_STATS_BKTS/2];

This actually did clean up some in some places but because the callback still uses a linear array of buckets we do get this:

-       if (cb->stat[READ].nr_samples)
-               q->poll_stat[READ] = cb->stat[READ];
-       if (cb->stat[WRITE].nr_samples)
-               q->poll_stat[WRITE] = cb->stat[WRITE];
+       for (bucket = 0; bucket < BLK_MQ_POLL_STATS_BKTS; bucket++) {
+               if (cb->stat[bucket].nr_samples)
+                       q->poll_stat[bucket%2][bucket/2] = cb->stat[bucket];

I tend to agree with Omar that keeping the buckets in a linear array is overall cleaner and more generalized.

However right now I am stuck as I am seeing the kernel oops I reported before in testing of my latest patchset [1]. I will try and find some time to bisect that but it looks like it was introduced when the support for mq schedulers was added (on or around bd166ef18).

Stephen

[1] http://marc.info/?l=linux-block&m=149156785215919&w=2