Re: [PATCH V2 10/20] blk-mq-sched: introduce helpers for query, change busy state

Jens Axboe
2017-08-23T20:02:20Z

On Tue, Aug 22 2017, Bart Van Assche wrote:
> On Sat, 2017-08-05 at 14:56 +0800, Ming Lei wrote:
> > +static inline bool blk_mq_hctx_is_dispatch_busy(struct blk_mq_hw_ctx *hctx)
> > +{
> > + return test_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state);
> > +}
> > +
> > +static inline void blk_mq_hctx_set_dispatch_busy(struct blk_mq_hw_ctx *hctx)
> > +{
> > + set_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state);
> > +}
> > +
> > +static inline void blk_mq_hctx_clear_dispatch_busy(struct blk_mq_hw_ctx *hctx)
> > +{
> > + clear_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state);
> > +}
>
> Hello Ming,
>
> Are these helper functions modified in a later patch? If not, please drop
> this patch. One line helper functions are not useful and do not improve
> readability of source code.

Agree, they just obfuscate the code. Only reason to do this is to do
things like:

static inline void blk_mq_hctx_clear_dispatch_busy(struct blk_mq_hw_ctx *hctx)
{
if (test_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state))
clear_bit(BLK_MQ_S_DISPATCH_BUSY, &hctx->state);
}

to avoid unecessary RMW (and locked instruction). At least then you can
add a single comment as to why it's done that way. Apart from that, I
prefer to open-code it so people don't have to grep to figure out wtf
blk_mq_hctx_clear_dispatch_busy() does.

--
Jens Axboe