linux-kernel - Re: [PATCH] riscv: Move call to init_cpu_topology() to later initialization stage

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Message-ID: <Y7Rg28suWh1RUbkU@spud>
Date:   Tue, 3 Jan 2023 17:07:39 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Leyfoon Tan <leyfoon.tan@...rfivetech.com>,
        Sudeep Holla <sudeep.holla@....com>
Cc:     Andrew Jones <ajones@...tanamicro.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ley Foon Tan <lftan.linux@...il.com>
Subject: Re: [PATCH] riscv: Move call to init_cpu_topology() to later
 initialization stage

Hello!

Couple comments for you.

+CC Sudeep: I've got a question for you below.

On Tue, Jan 03, 2023 at 07:53:38AM +0000, Leyfoon Tan wrote:
> > From: Andrew Jones <ajones@...tanamicro.com>
> > Subject: Re: [PATCH] riscv: Move call to init_cpu_topology() to later
> > initialization stage
> > On Tue, Jan 03, 2023 at 11:53:16AM +0800, Ley Foon Tan wrote:
> > > topology_parse_cpu_capacity() is failed to allocate memory with
> > > kcalloc() after read "capacity-dmips-mhz" DT parameter in CPU DT

Uhh, so where did this "capacity-dmips-mhz" property actually come from?
I had a quick check of qemu with grep & I don't see anything there that
would add this property.
This property should not be valid on anything other than arm AFAICT.

> > > nodes. This
> > > topology_parse_cpu_capacity() is called from init_cpu_topology(), move
> > > call to init_cpu_topology() to later initialization  stage (after
> > > memory allocation is available).
> > >
> > > Note, this refers to ARM64 implementation, call init_cpu_topology() in
> > > smp_prepare_cpus().
> > >
> > > Tested on Qemu platform.
> > 
> > Hi Ley,
> > 
> > Can you provide the topologies (command lines) tested?
> 2 clusters with 2 CPU cores each.

What's the actual commandline for this? I'm not the best with QEMU, so
it'd really be appreciated, given the above.

> > > Signed-off-by: Ley Foon Tan <leyfoon.tan@...rfivetech.com>
> > 
> > Fixes tag?
> Okay, will send out next revision with Fixes tag.

Please don't just send versions to add tags, Palmer can pick them up
if/when he applies the patch.

> Fixes: 03f11f03dbfe ("RISC-V: Parse cpu topology during boot. ")

> > >  arch/riscv/kernel/smpboot.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > > index 3373df413c88..ddb2afba6d25 100644
> > > --- a/arch/riscv/kernel/smpboot.c
> > > +++ b/arch/riscv/kernel/smpboot.c
> > > @@ -39,7 +39,6 @@ static DECLARE_COMPLETION(cpu_running);
> > >
> > >  void __init smp_prepare_boot_cpu(void)  {
> > > -	init_cpu_topology();
> > >  }
> > >
> > >  void __init smp_prepare_cpus(unsigned int max_cpus) @@ -48,6 +47,8
> > @@
> > > void __init smp_prepare_cpus(unsigned int max_cpus)
> > >  	int ret;
> > >  	unsigned int curr_cpuid;
> > >
> > > +	init_cpu_topology();

I know arm64 does this, but there is any real reason for us to do so?
@Sudeep, do you know why arm64 calls that each time?
Or if it is worth "saving" that call on riscv, since arm64 is clearly
happily calling it for many years & calling it later would likely head
off a good few allocation issues (like the one we saw with the topology
reworking a few months ago).

Thanks,
Conor.

> > > +
> > >  	curr_cpuid = smp_processor_id();
> > >  	store_cpu_topology(curr_cpuid);
> > >  	numa_store_cpu_info(curr_cpuid);
> > > --
> > > 2.25.1
> > >
> > 
> > Otherwise,
> > 
> > Reviewed-by: Andrew Jones <ajones@...tanamicro.com>


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