Re: [PATCH 05/16] blk-mq: allow software queue to map to multiple hardware queues
From: Jens Axboe
Date: Wed Oct 31 2018 - 10:19:17 EST
On 10/30/18 6:49 PM, Sagi Grimberg wrote:
>> @@ -2342,10 +2346,16 @@ static void blk_mq_map_swqueue(struct request_queue *q)
>> ctx = per_cpu_ptr(q->queue_ctx, i);
>> hctx = blk_mq_map_queue_type(q, 0, i);
>> + hctx->type = 0;
>> cpumask_set_cpu(i, hctx->cpumask);
>> - ctx->index_hw = hctx->nr_ctx;
>> + ctx->index_hw[hctx->type] = hctx->nr_ctx;
>> hctx->ctxs[hctx->nr_ctx++] = ctx;
>> + /*
>> + * If the nr_ctx type overflows, we have exceeded the
>> + * amount of sw queues we can support.
>> + */
>> + BUG_ON(!hctx->nr_ctx);
> Was this added because nr_ctx became short? What was the motivation
> for that? save space? structure alignment?
Right, I made it smaller to not take up more space after this change.
And since it is now smaller, adding a check for wrap seemed like
a good idea.
> Perhaps this should be mentioned in the change log (as it contradicts
> that no functional changes exist in this patch). Or, if this can happen
> even when 32bit nr_ctx, it should be a separate small patch?
Could happen for any type, but more likely now of course. I'll
mention this in the changelog.