| Message ID | 20210111044050.86763-1-dave@stgolabs.net (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | usb/c67x00: Replace tasklet with work | expand |
Hello! On 11.01.2021 7:40, Davidlohr Bueso wrote: > Tasklets have long been deprecated as being too heavy on the system > by running in irq context - and this is not a performance critical > path. If a higher priority process wants to run, it must wait for > the tasklet to finish before doing so. > > c67x00_do_work() will now run in process context and have further > concurrency (tasklets being serialized among themselves), but this > is done holding the c67x00->lock, so it should be fine. Furthermore, > this patch fixes the usage of the lock in the callback as otherwise > it would need to be irq-safe. > > Signed-off-by: Davidlohr Bueso <dbueso@suse.de> [...] > diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c > index e65f1a0ae80b..af60f4fdd340 100644 > --- a/drivers/usb/c67x00/c67x00-sched.c > +++ b/drivers/usb/c67x00/c67x00-sched.c > @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00) > > /* -------------------------------------------------------------------------- */ > > -static void c67x00_sched_tasklet(struct tasklet_struct *t) > +static void c67x00_sched_work(struct work_struct *work) > { > - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet); > + struct c67x00_hcd *c67x00; > + > + c67x00 = container_of(work, struct c67x00_hcd, work); > c67x00_do_work(c67x00); > } > > void c67x00_sched_kick(struct c67x00_hcd *c67x00) > { > - tasklet_hi_schedule(&c67x00->tasklet); > + queue_work(system_highpri_wq, &c67x00->work); Use a tab to indent, please. > } > > int c67x00_sched_start_scheduler(struct c67x00_hcd *c67x00) > { > - tasklet_setup(&c67x00->tasklet, c67x00_sched_tasklet); > + INIT_WORK(&c67x00->work, c67x00_sched_work); Here as well. > return 0; > } > > void c67x00_sched_stop_scheduler(struct c67x00_hcd *c67x00) > { > - tasklet_kill(&c67x00->tasklet); > + cancel_work_sync(&c67x00->work); And here. [...] MBR, Sergei
On Mon, 11 Jan 2021, Hillf Danton wrote: >On Sun, 10 Jan 2021 20:40:50 -0800 Davidlohr Bueso wrote: >> Tasklets have long been deprecated as being too heavy on the system >> by running in irq context - and this is not a performance critical >> path. If a higher priority process wants to run, it must wait for >> the tasklet to finish before doing so. >> >> c67x00_do_work() will now run in process context and have further >> concurrency (tasklets being serialized among themselves), but this >> is done holding the c67x00->lock, so it should be fine. Furthermore, >> this patch fixes the usage of the lock in the callback as otherwise >> it would need to be irq-safe. > >Can you add a couple of words about the need to be irq-safe because >no lock is taken for scheduling either tasklet or work? I was refering to the locking in the c67x00_do_work() tasklet callback. Because it is currently under irq it should be disabling irq (or at least BH) but after this patch that is no longer the case. >> >> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> >> --- >> drivers/usb/c67x00/c67x00-hcd.h | 2 +- >> drivers/usb/c67x00/c67x00-sched.c | 12 +++++++----- >> 2 files changed, 8 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/usb/c67x00/c67x00-hcd.h b/drivers/usb/c67x00/c67x00-hcd.h >> index 6b6b04a3fe0f..6332a6b5dce6 100644 >> --- a/drivers/usb/c67x00/c67x00-hcd.h >> +++ b/drivers/usb/c67x00/c67x00-hcd.h >> @@ -76,7 +76,7 @@ struct c67x00_hcd { >> u16 next_td_addr; >> u16 next_buf_addr; >> >> - struct tasklet_struct tasklet; >> + struct work_struct work; >> >> struct completion endpoint_disable; >> >> diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c >> index e65f1a0ae80b..af60f4fdd340 100644 >> --- a/drivers/usb/c67x00/c67x00-sched.c >> +++ b/drivers/usb/c67x00/c67x00-sched.c >> @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00) >> >> /* -------------------------------------------------------------------------- */ >> >> -static void c67x00_sched_tasklet(struct tasklet_struct *t) >> +static void c67x00_sched_work(struct work_struct *work) >> { >> - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet); >> + struct c67x00_hcd *c67x00; >> + >> + c67x00 = container_of(work, struct c67x00_hcd, work); >> c67x00_do_work(c67x00); >> } >> >> void c67x00_sched_kick(struct c67x00_hcd *c67x00) >> { >> - tasklet_hi_schedule(&c67x00->tasklet); >> + queue_work(system_highpri_wq, &c67x00->work); > >Better if one line comment is added for highpri, given this is not a >performance critical path. I'm not sure the value here, considering the highprio is not being changed here. There are a few drivers who use highpri workqueue and care about latencies but they are still not performance critical (to the overall system that is, which is what I meant by that). Thanks, Davidlohr
diff --git a/drivers/usb/c67x00/c67x00-hcd.h b/drivers/usb/c67x00/c67x00-hcd.h index 6b6b04a3fe0f..6332a6b5dce6 100644 --- a/drivers/usb/c67x00/c67x00-hcd.h +++ b/drivers/usb/c67x00/c67x00-hcd.h @@ -76,7 +76,7 @@ struct c67x00_hcd { u16 next_td_addr; u16 next_buf_addr; - struct tasklet_struct tasklet; + struct work_struct work; struct completion endpoint_disable; diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c index e65f1a0ae80b..af60f4fdd340 100644 --- a/drivers/usb/c67x00/c67x00-sched.c +++ b/drivers/usb/c67x00/c67x00-sched.c @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00) /* -------------------------------------------------------------------------- */ -static void c67x00_sched_tasklet(struct tasklet_struct *t) +static void c67x00_sched_work(struct work_struct *work) { - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet); + struct c67x00_hcd *c67x00; + + c67x00 = container_of(work, struct c67x00_hcd, work); c67x00_do_work(c67x00); } void c67x00_sched_kick(struct c67x00_hcd *c67x00) { - tasklet_hi_schedule(&c67x00->tasklet); + queue_work(system_highpri_wq, &c67x00->work); } int c67x00_sched_start_scheduler(struct c67x00_hcd *c67x00) { - tasklet_setup(&c67x00->tasklet, c67x00_sched_tasklet); + INIT_WORK(&c67x00->work, c67x00_sched_work); return 0; } void c67x00_sched_stop_scheduler(struct c67x00_hcd *c67x00) { - tasklet_kill(&c67x00->tasklet); + cancel_work_sync(&c67x00->work); }
Tasklets have long been deprecated as being too heavy on the system by running in irq context - and this is not a performance critical path. If a higher priority process wants to run, it must wait for the tasklet to finish before doing so. c67x00_do_work() will now run in process context and have further concurrency (tasklets being serialized among themselves), but this is done holding the c67x00->lock, so it should be fine. Furthermore, this patch fixes the usage of the lock in the callback as otherwise it would need to be irq-safe. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> --- drivers/usb/c67x00/c67x00-hcd.h | 2 +- drivers/usb/c67x00/c67x00-sched.c | 12 +++++++----- 2 files changed, 8 insertions(+), 6 deletions(-)