Messages in this thread | | | From | Guenter Roeck <> | Date | Wed, 22 Apr 2020 08:47:52 -0700 | Subject | Re: [PATCH 11/23] sched,spi: Convert to sched_set_fifo*() |
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On Wed, Apr 22, 2020 at 7:35 AM Doug Anderson <dianders@chromium.org> wrote: > > Hi, > > On Wed, Apr 22, 2020 at 6:56 AM Mark Brown <broonie@kernel.org> wrote: > > > > On Wed, Apr 22, 2020 at 01:27:30PM +0200, Peter Zijlstra wrote: > > > Because SCHED_FIFO is a broken scheduler model (see previous patches) > > > take away the priority field, the kernel can't possibly make an > > > informed decision. > > > > > > No effective change. > > > > Copying Doug who did this change and Guenter who reviewed it. This > > looks fine to me but I've no particular involvement with the code or > > platforms that are affected here. > > Thanks! Probably the maintainers of cros_ec_spi.c (Benson and Enric) > should be aware of it, too. CCing them. > > From my point of view, my response is pretty much identical to the one > I wrote when the priority was reduced from "MAX_RT_PRIO - 1" to > "MAX_RT_PRIO / 2" [1]. Basically, any priority that keeps us from > being preempted by tasks that are only high priority for performance > reasons (like dm crypt and loopback did when I last analyzed) is fine. > Our priority needs to be high not for performance reasons but for > correctness reasons (the other side will drop our data if we don't > respond in time). > The crypto engine ends up running at the same priority level, so I am a bit concerned that this patch series will re-introduce the problem that Doug's initial patch tried to solve. Though I do notice that it already _is_ running at the same priority, so maybe the problem has already been re-introduced with the commit that set the priority to MAX_RT_PRIO / 2, and we just haven't noticed yet. So I guess this patch indeed doesn't make a difference.
Reviewed-by: Guenter Roeck <groeck@chromium.org>
> Thus: > > Reviewed-by: Douglas Anderson <dianders@chromium.org> > > > [1] https://lore.kernel.org/r/CAD=FV=UsYF1R6+XRfFFFm6PfmkTsEOfxxgCw2JxCnpyu1kGVLQ@mail.gmail.com > > > > > Cc: broonie@kernel.org > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > > > Reviewed-by: Ingo Molnar <mingo@kernel.org> > > > --- > > > drivers/platform/chrome/cros_ec_spi.c | 6 +----- > > > 1 file changed, 1 insertion(+), 5 deletions(-) > > > > > > --- a/drivers/platform/chrome/cros_ec_spi.c > > > +++ b/drivers/platform/chrome/cros_ec_spi.c > > > @@ -709,9 +709,6 @@ static void cros_ec_spi_high_pri_release > > > static int cros_ec_spi_devm_high_pri_alloc(struct device *dev, > > > struct cros_ec_spi *ec_spi) > > > { > > > - struct sched_param sched_priority = { > > > - .sched_priority = MAX_RT_PRIO / 2, > > > - }; > > > int err; > > > > > > ec_spi->high_pri_worker = > > > @@ -728,8 +725,7 @@ static int cros_ec_spi_devm_high_pri_all > > > if (err) > > > return err; > > > > > > - err = sched_setscheduler_nocheck(ec_spi->high_pri_worker->task, > > > - SCHED_FIFO, &sched_priority); > > > + err = sched_set_fifo(ec_spi->high_pri_worker->task); > > > if (err) > > > dev_err(dev, "Can't set cros_ec high pri priority: %d\n", err); > > > return err; > > > --- a/drivers/spi/spi.c > > > +++ b/drivers/spi/spi.c > > > @@ -1589,11 +1589,9 @@ EXPORT_SYMBOL_GPL(spi_take_timestamp_pos > > > */ > > > static void spi_set_thread_rt(struct spi_controller *ctlr) > > > { > > > - struct sched_param param = { .sched_priority = MAX_RT_PRIO / 2 }; > > > - > > > dev_info(&ctlr->dev, > > > "will run message pump with realtime priority\n"); > > > - sched_setscheduler(ctlr->kworker_task, SCHED_FIFO, ¶m); > > > + sched_set_fifo(ctlr->kworker_task); > > > } > > > > > > static int spi_init_queue(struct spi_controller *ctlr) > > > > > >
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