Message-ID: <CAOnJCULo2gwLYCPdMppwhZekbuLh7FydjO7T1ZvJ0C8VG559YQ@mail.gmail.com>
Date: Tue, 9 Jul 2024 14:43:37 -0700
From: Atish Patra <atishp@...shpatra.org>
To: Conor Dooley <conor@...nel.org>
Cc: Charlie Jenkins <charlie@...osinc.com>, Xiao Wang <xiao.w.wang@...el.com>, 
	Alexandre Ghiti <alexghiti@...osinc.com>, paul.walmsley@...ive.com, palmer@...belt.com, 
	aou@...s.berkeley.edu, anup@...infault.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/perf: riscv: Remove redundant macro check

On Tue, Jul 9, 2024 at 2:05 PM Conor Dooley <conor@...nel.org> wrote:
>
> On Tue, Jul 09, 2024 at 01:57:47PM -0700, Charlie Jenkins wrote:
> > On Tue, Jul 09, 2024 at 09:44:17PM +0100, Conor Dooley wrote:
> > > On Tue, Jul 09, 2024 at 01:29:42PM -0700, Charlie Jenkins wrote:
> > > > On Mon, Jul 08, 2024 at 01:22:11PM +0100, Conor Dooley wrote:
> > > > > On Mon, Jul 08, 2024 at 08:12:24PM +0800, Xiao Wang wrote:
> > > > > > The macro CONFIG_RISCV_PMU must have been defined when riscv_pmu.c gets
> > > > > > compiled, so this patch removes the redundant check.
> > > > >
> > > > > Did you investigate why this define was added? Why do you think that it
> > > > > is redundant, rather than checking the incorrect config option?
> > > >
> > > > This file is only compiled with CONFIG_RISCV_PMU:
> > >
> > > I might be ill, but I can still read. I was not disagreeing with Xiao
> > > that the condition is redundant as written - I want to know whether they
> > > made sure that this check was intentionally using CONFIG_RISCV_PMU in the
> > > first place, or if another option should have been here instead.
> >
> > Makes sense! Looking through the lists I see this RFC from Atish where
> > he introduced a different config option for this
> > "CONFIG_RISCV_PMU_COMMON"[1]. I wonder if something got confused in the
> > development of these two patches.
>

Nope. That's not related as the above series is a complete revamp of
PMU infrastructure
and far from being merged.

> Perhaps.. What I was worried about was the wrong option being here
> (maybe that it should have been RISCV_PMU_SBI or similar) and depending
> on how the kernel is configured, userspace would get the wrong info
> here. But maybe it is innocuous your theory would suggest, and there's
> nothing to worry about. But that's for someone with a functioning brain
> to figure out ;)
>
This macro has been there since v3 of the original series.
https://lore.kernel.org/lkml/20230802080328.1213905-8-alexghiti@rivosinc.com/

Ideally, this should have been RISCV_PMU_SBI as ctr_get_width was not
defined earlier for legacy.
However, that was fixed here
https://lore.kernel.org/lkml/20240227170002.188671-3-vadim.shakirov@syntacore.com/

So we can remove the macro check here.

Reviewed-by: Atish Patra <atishp@...osinc.com>

> Cheers,
> Conor.
>
> >
> > Link:
> > https://lore.kernel.org/lkml/20240217005738.3744121-12-atishp@rivosinc.com/
> > [1]
> >
> > > > # drivers/perf/Makefile
> > > > obj-$(CONFIG_RISCV_PMU) += riscv_pmu.o
> > > >
> > > > So having this check does seem redundant. I am copying Alex as it looks
> > > > like he wrote this.
> > > >
> > > > > >
> > > > > > Signed-off-by: Xiao Wang <xiao.w.wang@...el.com>
> > > > > > ---
> > > > > >  drivers/perf/riscv_pmu.c | 2 --
> > > > > >  1 file changed, 2 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/perf/riscv_pmu.c b/drivers/perf/riscv_pmu.c
> > > > > > index 0a02e85a8951..7644147d50b4 100644
> > > > > > --- a/drivers/perf/riscv_pmu.c
> > > > > > +++ b/drivers/perf/riscv_pmu.c
> > > > > > @@ -39,7 +39,6 @@ void arch_perf_update_userpage(struct perf_event *event,
> > > > > >       userpg->cap_user_time_short = 0;
> > > > > >       userpg->cap_user_rdpmc = riscv_perf_user_access(event);
> > > > > >
> > > > > > -#ifdef CONFIG_RISCV_PMU
> > > > > >       /*
> > > > > >        * The counters are 64-bit but the priv spec doesn't mandate all the
> > > > > >        * bits to be implemented: that's why, counter width can vary based on
> > > > > > @@ -47,7 +46,6 @@ void arch_perf_update_userpage(struct perf_event *event,
> > > > > >        */
> > > > > >       if (userpg->cap_user_rdpmc)
> > > > > >               userpg->pmc_width = to_riscv_pmu(event->pmu)->ctr_get_width(event->hw.idx) + 1;
> > > > > > -#endif
> > > > > >
> > > > > >       do {
> > > > > >               rd = sched_clock_read_begin(&seq);
> > > > > > --
> > > > > > 2.25.1
> > > > > >
> > > > > >
> > > > > > _______________________________________________
> > > > > > linux-riscv mailing list
> > > > > > linux-riscv@...ts.infradead.org
> > > > > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > > >
> >
> >



-- 
Regards,
Atish

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