On Tue, May 10, 2016 at 01:46:13PM +0800, Simon Guo wrote:
> Hi,
> On Mon, May 09, 2016 at 05:22:15PM -0700, Shaohua Li wrote:
> > if trace isn't enabled, parsing cgroup path just wastes cpu
> >
> > Signed-off-by: Shaohua Li <shli@xxxxxx>
> > ---
> > block/blk-throttle.c | 5 ++---
> > include/linux/blktrace_api.h | 9 +++++++++
> > 2 files changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/block/blk-throttle.c b/block/blk-throttle.c
> > index 2149a1d..47a3e54 100644
> > --- a/block/blk-throttle.c
> > +++ b/block/blk-throttle.c
> > @@ -211,15 +211,14 @@ static struct throtl_data *sq_to_td(struct throtl_service_queue *sq)
> > *
> > * The messages are prefixed with "throtl BLKG_NAME" if @sq belongs to a
> > * throtl_grp; otherwise, just "throtl".
> > - *
> > - * TODO: this should be made a function and name formatting should happen
> > - * after testing whether blktrace is enabled.
> > */
> > #define throtl_log(sq, fmt, args...) do { \
> > struct throtl_grp *__tg = sq_to_tg((sq)); \
> > struct throtl_data *__td = sq_to_td((sq)); \
> > \
> > (void)__td; \
> > + if (likely(!blk_trace_note_message_enabled(__td->queue))) \
> > + break; \
> > if ((__tg)) { \
> > char __pbuf[128]; \
> > \
> > diff --git a/include/linux/blktrace_api.h b/include/linux/blktrace_api.h
> > index afc1343..0f3172b 100644
> > --- a/include/linux/blktrace_api.h
> > +++ b/include/linux/blktrace_api.h
> > @@ -57,6 +57,14 @@ void __trace_note_message(struct blk_trace *, const char *fmt, ...);
> > } while (0)
> > #define BLK_TN_MAX_MSG 128
> >
> > +static inline bool blk_trace_note_message_enabled(struct request_queue *q)
> > +{
> > + struct blk_trace *bt = q->blk_trace;
> > + if (likely(!bt))
> > + return false;
> > + return bt->act_mask & BLK_TC_NOTIFY;
> > +}
> Is there any reason to skip following condition?
> if (unlikely(bt->trace_state != Blktrace_running &&
> !blk_tracer_enabled))
It's marked unlikely and to add the check we must export
blk_tracer_enabled, so I ignored it. Though I don't know how unlikely it
is.
Thanks,
Shaohua
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