linux-kernel - RE: [PATCH v3] cpu-topology: Skip the exist but not possible cpu nodes

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Date:   Fri, 17 Jan 2020 01:32:33 +0000
From:   "Zengtao (B)" <prime.zeng@...ilicon.com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     Linuxarm <linuxarm@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3] cpu-topology: Skip the exist but not possible cpu
 nodes

> -----Original Message-----
> From: Sudeep Holla [mailto:sudeep.holla@....com]
> Sent: Thursday, January 16, 2020 8:25 PM
> To: Zengtao (B)
> Cc: Linuxarm; Greg Kroah-Hartman; Rafael J. Wysocki; Sudeep Holla;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v3] cpu-topology: Skip the exist but not possible cpu
> nodes
> 
> Sorry for being pedantic and not mentioning this earlier. Can you
> improve
> the $subject. I prefer:
> 
> cpu-topology: Don't error on more than CONFIG_NR_CPUS CPUs in
> device tree
> 
> On Thu, Jan 16, 2020 at 09:47:35AM +0800, Zeng Tao wrote:
> > When CONFIG_NR_CPUS is smaller than the cpu nodes defined in the
> device
> > tree, all the cpu nodes parsing will fail.
> > And this is not reasonable for a legal device tree configs.
> > In this patch, skip such cpu nodes rather than return an error.
> >
> 
> Also the commit log to be:
> "
> When the kernel is configured with CONFIG_NR_CPUS smaller than the
> number of CPU nodes in the device tree(DT), all the CPU nodes parsing
> done to fetch topology information will fail. This is not reasonable
> as it is legal to have all the physical CPUs in the system in the DT.
> 
> Let us just skip such CPU DT nodes that are not used in the kernel
> rather than returning an error.
> "
> > Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
> > ---
> > Changelog:
> > v2->v3:
> >  -Fix the Review comments by sudeep, including fix typo, remove
> redundant check
> >  logic, change the warning print level etc.
> > v1->v2:
> >  -Remove redundant -ENODEV assignment in get_cpu_for_node
> >  -Add comment to describe the get_cpu_for_node return values
> >  -Add skip process for cpu threads
> >  -Update the commit log with more detail
> > ---
> >  drivers/base/arch_topology.c | 20 +++++++++++++++-----
> >  1 file changed, 15 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/base/arch_topology.c
> b/drivers/base/arch_topology.c
> > index 5fe44b3..d4302a1 100644
> > --- a/drivers/base/arch_topology.c
> > +++ b/drivers/base/arch_topology.c
> > @@ -248,6 +248,16 @@ core_initcall(free_raw_capacity);
> >  #endif
> >
> >  #if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
> > +/*
> > + * This function returns the logic cpu number of the node.
> > + * There are basically three kinds of return values:
> > + * (1) logic cpu number which is > 0.
> > + * (2) -ENODEV when the node is valid one which can be found in the
> device tree
> > + * but there is no possible cpu nodes to match, when the
> CONFIG_NR_CPUS is
> > + * smaller than cpus node numbers in device tree, this will happen.
> It's
> > + * suggested to just ignore this case.
> 
> I prefer (2) to be reword as below:
> "
> -ENODEV when the device tree(DT) node is valid and found in the DT but
> there is no possible logical CPU in the kernel to match. This happens
> when CONFIG_NR_CPUS is configure to be smaller than the number of
> CPU
> nodes in DT. We need to just ignore this case.
> "
> 
> With all these changes you can stick:
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> 
OK, I will take the above suggestions, thanks for the patience, ^_^

Regards
Zengtao 
> --
> Regards,
> Sudeep