Messages in this thread | | | Date | Mon, 8 Jun 2020 09:33:42 -0700 | From | Christoph Hellwig <> | Subject | Re: blk-softirq vs smp_call_function_single_async() |
| |
On Mon, Jun 08, 2020 at 05:58:33PM +0200, Peter Zijlstra wrote: > > A request can only be completed once. > > Sure, but that doesn't help. > > CPU0 CPU1 > > raise_blk_irq() BLOCK_SOFTIRQ > IPI -> CPU1 > > // picks up thing from CPU0 > req->complete(req); > > > <big hole where CSD is active and request completed> > > <IPI> > trigger_softirq() > > > What happens to a struct request after completion, is it free()d > or reused? If reused, how do we guarantee CSD completion before > free()ing?
The request is freed in the block layer sense by __blk_mq_free_request (which doesn't actually free the memory, so it eventually gets reused).
__blk_mq_free_request is called from blk_mq_end_request which is called from the drivers ->complete_rq method, which is called from the block softirq.
What is the method to guaranteed CSD completion?
| |