Re: [PATCH RFC 10/14] block, bfq: add Early Queue Merge (EQM)
From: Jens Axboe <axboe@kernel.dk>
Date: 2017-03-07 19:34:55
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lkml
On 03/04/2017 09:01 AM, Paolo Valente wrote:
quoted hunk ↗ jump to hunk
@@ -560,6 +600,15 @@ struct bfq_data { struct bfq_io_cq *bio_bic; /* bfqq associated with the task issuing current bio for merging */ struct bfq_queue *bio_bfqq; + + /* + * io context to put right after bfqd->lock is released. This + * filed is used to perform put_io_context, when needed, to + * after the scheduler lock has been released, and thus + * prevent an ioc->lock from being possibly taken while the + * scheduler lock is being held. + */ + struct io_context *ioc_to_put; };
The logic around this is nasty, effectively you end up having locking around sections of code instea of structures, which is never a good idea. The helper functions for unlocking and dropping the ioc add to the mess as well. Can't we simply pass back a pointer to an ioc to free? That should be possible, given that we must have grabbed the bfqd lock ourselves further up in the call chain. So we _know_ that we'll drop it later on. If that wasn't the case, the existing logic wouldn't work. -- Jens Axboe