Messages in this thread | | | Subject | Re: [PATCH 1/1] char: hpet: Remove unused local variable 'm' in hpet_interrupt() | From | "Leizhen (ThunderTown)" <> | Date | Fri, 16 Apr 2021 10:08:25 +0800 |
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On 2021/4/15 22:53, Greg Kroah-Hartman wrote: > On Thu, Apr 15, 2021 at 10:24:04PM +0800, Zhen Lei wrote: >> Commit 273ef9509b79 ("drivers/char/hpet.c: fix periodic-emulation for >> delayed interrupt") removed the reference to local variable 'm', but >> forgot to remove the definition and assignment of it. Due to >> read_counter() indirectly calls "read barrier", the performance is >> slightly degraded. >> >> Since the following comments give some description based on 'm', so move >> the assignment of 'm' into it. >> >> Fixes: 273ef9509b79 ("drivers/char/hpet.c: fix periodic-emulation for delayed interrupt") >> Reported-by: Hulk Robot <hulkci@huawei.com> >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> --- >> drivers/char/hpet.c | 8 +++++--- >> 1 file changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c >> index ed3b7dab678dbd1..46950a0cda181a1 100644 >> --- a/drivers/char/hpet.c >> +++ b/drivers/char/hpet.c >> @@ -156,14 +156,16 @@ static irqreturn_t hpet_interrupt(int irq, void *data) >> * This has the effect of treating non-periodic like periodic. >> */ >> if ((devp->hd_flags & (HPET_IE | HPET_PERIODIC)) == HPET_IE) { >> - unsigned long m, t, mc, base, k; >> + unsigned long t, mc, base, k; >> struct hpet __iomem *hpet = devp->hd_hpet; >> struct hpets *hpetp = devp->hd_hpets; >> >> t = devp->hd_ireqfreq; >> - m = read_counter(&devp->hd_timer->hpet_compare); >> mc = read_counter(&hpet->hpet_mc); >> - /* The time for the next interrupt would logically be t + m, >> + /* >> + * m = read_counter(&devp->hd_timer->hpet_compare); > > Why did you comment this out? > > And are you sure that yuou are not required to actually read that > counter, even if you do not do anything with the value? Lots of > hardware works in odd ways... > > Have you tested and verified that this still works properly?
Sorry, I didn't actually test it. I didn't see any dependency on this read operation for other members' reads and writes. If this read operation is potentially required, hopefully there is an explanatory note next to it.
> > thanks, > > greg k-h > > . >
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