On Wed, 2014-02-05 at 04:39 -0800, Christoph Hellwig wrote:
> Avoid hitting the host-wide free_list lock unless we need to put a command
> back onto the freelist.
This one looks like it can go independently on its own.
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> drivers/scsi/scsi.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index ebcea6c..4139486 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -320,15 +320,16 @@ void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd,
> {
> unsigned long flags;
>
> - /* changing locks here, don't need to restore the irq state */
> - spin_lock_irqsave(&shost->free_list_lock, flags);
> if (unlikely(list_empty(&shost->free_list))) {
> - list_add(&cmd->list, &shost->free_list);
> - cmd = NULL;
> + spin_lock_irqsave(&shost->free_list_lock, flags);
> + if (list_empty(&shost->free_list)) {
> + list_add(&cmd->list, &shost->free_list);
> + cmd = NULL;
> + }
> + spin_unlock_irqrestore(&shost->free_list_lock, flags);
> }
> - spin_unlock_irqrestore(&shost->free_list_lock, flags);
>
> - if (likely(cmd != NULL))
> + if (cmd)
Why do this? cmd is still likely to be not NULL, which helps the
compiler optimise.
James
> scsi_pool_free_command(shost->cmd_pool, cmd);
>
> put_device(dev);
> --
> 1.7.10.4
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