From: Atish Patra <atish.patra@wdc.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>,
Dmitriy Cherkasov <dmitriy@oss-tech.org>,
Andreas Schwab <schwab@suse.de>,
Palmer Dabbelt <palmer@sifive.com>,
Johan Hovold <johan@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Paul Walmsley <paul.walmsley@sifive.com>,
Anup Patel <anup@brainfault.org>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>
Subject: Re: [PATCH v2 3/4] RISC-V: Implement nosmp commandline option.
Date: Thu, 11 Apr 2019 11:42:08 -0700 [thread overview]
Message-ID: <fbc18e77-f75c-6f34-2f2e-b461807ba910@wdc.com> (raw)
In-Reply-To: <20190411070119.GD29422@infradead.org>
On 4/11/19 12:01 AM, Christoph Hellwig wrote:
> On Wed, Apr 10, 2019 at 04:04:42PM -0700, Atish Patra wrote:
>> nosmp command line option sets max_cpus to zero. No secondary harts
>> will boot if this is enabled. But present cpu mask will still point to
>> all possible masks.
>>
>> Fix present cpu mask for nosmp usecase.
>>
>> Signed-off-by: Atish Patra <atish.patra@wdc.com>
>> ---
>> arch/riscv/kernel/smpboot.c | 12 +++++++++++-
>> 1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
>> index eb533b5c2c8c..a8ad200581aa 100644
>> --- a/arch/riscv/kernel/smpboot.c
>> +++ b/arch/riscv/kernel/smpboot.c
>> @@ -47,6 +47,17 @@ void __init smp_prepare_boot_cpu(void)
>>
>> void __init smp_prepare_cpus(unsigned int max_cpus)
>> {
>> + int cpuid;
>> +
>> + /* This covers non-smp usecase mandated by "nosmp" option */
>> + if (max_cpus == 0)
>> + return;
>> +
>> + for_each_possible_cpu(cpuid) {
>> + if (cpuid == smp_processor_id())
>> + continue;
>> + set_cpu_present(cpuid, true);
>> + }
>
> Most other architectures seem to use init_cpu_present() here.
>
I did a quick grep through other archs. Mostly, init_cpu_present is
preferred when you update a entire cpumask or cpu 0.
We can just use cpu_possible_mask and init_cpu_present together to avoid
the loop. It will just set the current boot cpu bit once more.
But looking at ARM64 code, we may have to bring back the loop when we
have some implementation similar cpu_ops.
Regards,
Atish
> Otherwise this looks fine to me.
>
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next prev parent reply other threads:[~2019-04-11 18:42 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 23:04 [PATCH v2 0/4] Miscellaneous kernel command line fixes Atish Patra
2019-04-10 23:04 ` [PATCH v2 1/4] RISC-V: Add RISC-V specific arch_match_cpu_phys_id Atish Patra
2019-04-11 6:58 ` Christoph Hellwig
2019-04-10 23:04 ` [PATCH v2 2/4] RISC-V: Fix of_get_cpu_node usage Atish Patra
2019-04-11 6:59 ` Christoph Hellwig
2019-04-11 18:14 ` Atish Patra
2019-04-10 23:04 ` [PATCH v2 3/4] RISC-V: Implement nosmp commandline option Atish Patra
2019-04-11 7:01 ` Christoph Hellwig
2019-04-11 18:42 ` Atish Patra [this message]
2019-04-10 23:04 ` [PATCH v2 4/4] RISC-V: Support nr_cpus command line option Atish Patra
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