* [PATCH] RISC-V: Do not issue remote fences until smp is available
@ 2022-10-28 23:19 Atish Patra
2022-10-31 19:11 ` Conor Dooley
0 siblings, 1 reply; 5+ messages in thread
From: Atish Patra @ 2022-10-28 23:19 UTC (permalink / raw)
To: linux-kernel
Cc: Atish Patra, Albert Ou, Atish Patra, Anup Patel, Damien Le Moal,
devicetree, Jisheng Zhang, Krzysztof Kozlowski, linux-riscv,
Palmer Dabbelt, Paul Walmsley, Rob Herring
It is useless to issue remote fences if there is a single core
available. It becomes a bottleneck for sbi based rfences where
we will be making those ECALLs for no reason. Early code patching
because of static calls end up in this path.
Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
arch/riscv/mm/cacheflush.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
index f10cb47eac3a..7fafc8c26505 100644
--- a/arch/riscv/mm/cacheflush.c
+++ b/arch/riscv/mm/cacheflush.c
@@ -19,6 +19,10 @@ void flush_icache_all(void)
{
local_flush_icache_all();
+ /* No need to issue remote fence if only 1 cpu is online */
+ if (num_online_cpus() == 1)
+ return;
+
if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
sbi_remote_fence_i(NULL);
else
--
2.34.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] RISC-V: Do not issue remote fences until smp is available
2022-10-28 23:19 [PATCH] RISC-V: Do not issue remote fences until smp is available Atish Patra
@ 2022-10-31 19:11 ` Conor Dooley
2022-10-31 19:26 ` Atish Patra
0 siblings, 1 reply; 5+ messages in thread
From: Conor Dooley @ 2022-10-31 19:11 UTC (permalink / raw)
To: Atish Patra
Cc: linux-kernel, Albert Ou, Atish Patra, Anup Patel, Damien Le Moal,
devicetree, Jisheng Zhang, Krzysztof Kozlowski, linux-riscv,
Palmer Dabbelt, Paul Walmsley, Rob Herring
On Fri, Oct 28, 2022 at 04:19:29PM -0700, Atish Patra wrote:
> It is useless to issue remote fences if there is a single core
> available. It becomes a bottleneck for sbi based rfences where
> we will be making those ECALLs for no reason. Early code patching
> because of static calls end up in this path.
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
Hey Atish,
This doesn't apply for me to either fixes or for-next. What branch does
it apply to?
Thanks,
Conor.
> ---
> arch/riscv/mm/cacheflush.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index f10cb47eac3a..7fafc8c26505 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -19,6 +19,10 @@ void flush_icache_all(void)
> {
> local_flush_icache_all();
>
> + /* No need to issue remote fence if only 1 cpu is online */
> + if (num_online_cpus() == 1)
> + return;
> +
> if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
> sbi_remote_fence_i(NULL);
> else
> --
> 2.34.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] RISC-V: Do not issue remote fences until smp is available
2022-10-31 19:11 ` Conor Dooley
@ 2022-10-31 19:26 ` Atish Patra
2022-11-10 21:42 ` Palmer Dabbelt
0 siblings, 1 reply; 5+ messages in thread
From: Atish Patra @ 2022-10-31 19:26 UTC (permalink / raw)
To: Conor Dooley
Cc: Atish Patra, linux-kernel, Albert Ou, Anup Patel, Damien Le Moal,
devicetree, Jisheng Zhang, Krzysztof Kozlowski, linux-riscv,
Palmer Dabbelt, Paul Walmsley, Rob Herring
On Mon, Oct 31, 2022 at 12:12 PM Conor Dooley <conor@kernel.org> wrote:
>
> On Fri, Oct 28, 2022 at 04:19:29PM -0700, Atish Patra wrote:
> > It is useless to issue remote fences if there is a single core
> > available. It becomes a bottleneck for sbi based rfences where
> > we will be making those ECALLs for no reason. Early code patching
> > because of static calls end up in this path.
> >
> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
>
> Hey Atish,
> This doesn't apply for me to either fixes or for-next. What branch does
> it apply to?
> Thanks,
> Conor.
>
> > ---
> > arch/riscv/mm/cacheflush.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index f10cb47eac3a..7fafc8c26505 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -19,6 +19,10 @@ void flush_icache_all(void)
> > {
> > local_flush_icache_all();
> >
> > + /* No need to issue remote fence if only 1 cpu is online */
> > + if (num_online_cpus() == 1)
> > + return;
> > +
> > if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
> > sbi_remote_fence_i(NULL);
> > else
> > --
> > 2.34.1
> >
Sorry I forgot to specify the dependencies for this patch. This patch
is based on Anup's IPI series [1] as
I assumed the IPI series would go first. I can rebase on top of the
master if required.
However, the issue will manifest only after Jisheng's patch[2] which
moved the sbi_init to earlier and introduced the
static key in the paging_init path.
[1] https://patchwork.kernel.org/project/linux-riscv/patch/20220820065446.389788-8-apatel@ventanamicro.com/
[2] https://lore.kernel.org/lkml/20220716115059.3509-1-jszhang@kernel.org/
--
Regards,
Atish
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] RISC-V: Do not issue remote fences until smp is available
2022-10-31 19:26 ` Atish Patra
@ 2022-11-10 21:42 ` Palmer Dabbelt
2022-11-12 7:46 ` Atish Patra
0 siblings, 1 reply; 5+ messages in thread
From: Palmer Dabbelt @ 2022-11-10 21:42 UTC (permalink / raw)
To: atishp
Cc: Conor Dooley, Atish Patra, linux-kernel, aou, anup,
damien.lemoal, devicetree, jszhang, krzysztof.kozlowski,
linux-riscv, Paul Walmsley, robh+dt
On Mon, 31 Oct 2022 12:26:05 PDT (-0700), atishp@atishpatra.org wrote:
> On Mon, Oct 31, 2022 at 12:12 PM Conor Dooley <conor@kernel.org> wrote:
>>
>> On Fri, Oct 28, 2022 at 04:19:29PM -0700, Atish Patra wrote:
>> > It is useless to issue remote fences if there is a single core
>> > available. It becomes a bottleneck for sbi based rfences where
>> > we will be making those ECALLs for no reason. Early code patching
>> > because of static calls end up in this path.
>> >
>> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
>>
>> Hey Atish,
>> This doesn't apply for me to either fixes or for-next. What branch does
>> it apply to?
>> Thanks,
>> Conor.
>>
>> > ---
>> > arch/riscv/mm/cacheflush.c | 4 ++++
>> > 1 file changed, 4 insertions(+)
>> >
>> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
>> > index f10cb47eac3a..7fafc8c26505 100644
>> > --- a/arch/riscv/mm/cacheflush.c
>> > +++ b/arch/riscv/mm/cacheflush.c
>> > @@ -19,6 +19,10 @@ void flush_icache_all(void)
>> > {
>> > local_flush_icache_all();
>> >
>> > + /* No need to issue remote fence if only 1 cpu is online */
>> > + if (num_online_cpus() == 1)
>> > + return;
>> > +
>> > if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
>> > sbi_remote_fence_i(NULL);
>> > else
>> > --
>> > 2.34.1
>> >
>
> Sorry I forgot to specify the dependencies for this patch. This patch
> is based on Anup's IPI series [1] as
> I assumed the IPI series would go first. I can rebase on top of the
> master if required.
> However, the issue will manifest only after Jisheng's patch[2] which
> moved the sbi_init to earlier and introduced the
> static key in the paging_init path.
>
> [1] https://patchwork.kernel.org/project/linux-riscv/patch/20220820065446.389788-8-apatel@ventanamicro.com/
> [2] https://lore.kernel.org/lkml/20220716115059.3509-1-jszhang@kernel.org/
IMO we should just stop issuing the SBI remote fences at all, with the
code to do IPI-based fences we're just adding complexity for the slow
case.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] RISC-V: Do not issue remote fences until smp is available
2022-11-10 21:42 ` Palmer Dabbelt
@ 2022-11-12 7:46 ` Atish Patra
0 siblings, 0 replies; 5+ messages in thread
From: Atish Patra @ 2022-11-12 7:46 UTC (permalink / raw)
To: Palmer Dabbelt
Cc: Conor Dooley, Atish Patra, linux-kernel, aou, anup,
damien.lemoal, devicetree, jszhang, linux-riscv, Paul Walmsley,
robh+dt
On Thu, Nov 10, 2022 at 1:42 PM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Mon, 31 Oct 2022 12:26:05 PDT (-0700), atishp@atishpatra.org wrote:
> > On Mon, Oct 31, 2022 at 12:12 PM Conor Dooley <conor@kernel.org> wrote:
> >>
> >> On Fri, Oct 28, 2022 at 04:19:29PM -0700, Atish Patra wrote:
> >> > It is useless to issue remote fences if there is a single core
> >> > available. It becomes a bottleneck for sbi based rfences where
> >> > we will be making those ECALLs for no reason. Early code patching
> >> > because of static calls end up in this path.
> >> >
> >> > Signed-off-by: Atish Patra <atishp@rivosinc.com>
> >>
> >> Hey Atish,
> >> This doesn't apply for me to either fixes or for-next. What branch does
> >> it apply to?
> >> Thanks,
> >> Conor.
> >>
> >> > ---
> >> > arch/riscv/mm/cacheflush.c | 4 ++++
> >> > 1 file changed, 4 insertions(+)
> >> >
> >> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> >> > index f10cb47eac3a..7fafc8c26505 100644
> >> > --- a/arch/riscv/mm/cacheflush.c
> >> > +++ b/arch/riscv/mm/cacheflush.c
> >> > @@ -19,6 +19,10 @@ void flush_icache_all(void)
> >> > {
> >> > local_flush_icache_all();
> >> >
> >> > + /* No need to issue remote fence if only 1 cpu is online */
> >> > + if (num_online_cpus() == 1)
> >> > + return;
> >> > +
> >> > if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
> >> > sbi_remote_fence_i(NULL);
> >> > else
> >> > --
> >> > 2.34.1
> >> >
> >
> > Sorry I forgot to specify the dependencies for this patch. This patch
> > is based on Anup's IPI series [1] as
> > I assumed the IPI series would go first. I can rebase on top of the
> > master if required.
> > However, the issue will manifest only after Jisheng's patch[2] which
> > moved the sbi_init to earlier and introduced the
> > static key in the paging_init path.
> >
> > [1] https://patchwork.kernel.org/project/linux-riscv/patch/20220820065446.389788-8-apatel@ventanamicro.com/
> > [2] https://lore.kernel.org/lkml/20220716115059.3509-1-jszhang@kernel.org/
>
> IMO we should just stop issuing the SBI remote fences at all, with the
> code to do IPI-based fences we're just adding complexity for the slow
> case.
Sure. We can do that too. However, that will have some performance
impact for any platform(existing and future ones) without imsic.
Is that acceptable ? Maybe it will encourage every vendor to implement
AIA instead of PLIC ;)
--
Regards,
Atish
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-11-12 7:46 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-10-28 23:19 [PATCH] RISC-V: Do not issue remote fences until smp is available Atish Patra
2022-10-31 19:11 ` Conor Dooley
2022-10-31 19:26 ` Atish Patra
2022-11-10 21:42 ` Palmer Dabbelt
2022-11-12 7:46 ` Atish Patra
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).