Re: [PATCH 4/7] block/nvme: switch to a NVMeRequest freelist

[Sergio Lopez]

On Tue, May 19, 2020 at 06:11:35PM +0100, Stefan Hajnoczi wrote:
> There are three issues with the current NVMeRequest->busy field:
> 1. The busy field is accidentally accessed outside q->lock when request
>    submission fails.
> 2. Waiters on free_req_queue are not woken when a request is returned
>    early due to submission failure.
> 2. Finding a free request involves scanning all requests. This makes
>    request submission O(n^2).
> 
> Switch to an O(1) freelist that is always accessed under the lock.
> 
> Also differentiate between NVME_QUEUE_SIZE, the actual SQ/CQ size, and
> NVME_NUM_REQS, the number of usable requests. This makes the code
> simpler than using NVME_QUEUE_SIZE everywhere and having to keep in mind
> that one slot is reserved.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
>  block/nvme.c | 81 ++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 54 insertions(+), 27 deletions(-)

Reviewed-by: Sergio Lopez <address@hidden>

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