From: Michael Ellerman <mpe@ellerman•id.au>
To: Kajol Jain <kjain@linux•ibm.com>, linuxppc-dev@lists•ozlabs.org
Cc: nathanl@linux•ibm.com, ego@linux•vnet.ibm.com,
maddy@linux•vnet.ibm.com, kjain@linux•ibm.com, suka@us•ibm.com,
anju@linux•vnet.ibm.com
Subject: Re: [PATCH v3 1/2] powerpc/perf/hv-24x7: Add cpu hotplug support
Date: Mon, 06 Jul 2020 13:13:16 +1000 [thread overview]
Message-ID: <87zh8d5oab.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <20200626102824.270923-2-kjain@linux.ibm.com>
Kajol Jain <kjain@linux•ibm.com> writes:
> Patch here adds cpu hotplug functions to hv_24x7 pmu.
> A new cpuhp_state "CPUHP_AP_PERF_POWERPC_HV_24x7_ONLINE" enum
> is added.
>
> The online callback function updates the cpumask only if its
> empty. As the primary intention of adding hotplug support
> is to designate a CPU to make HCALL to collect the
> counter data.
>
> The offline function test and clear corresponding cpu in a cpumask
> and update cpumask to any other active cpu.
>
> Signed-off-by: Kajol Jain <kjain@linux•ibm.com>
> Reviewed-by: Gautham R. Shenoy <ego@linux•vnet.ibm.com>
> ---
> arch/powerpc/perf/hv-24x7.c | 45 +++++++++++++++++++++++++++++++++++++
> include/linux/cpuhotplug.h | 1 +
> 2 files changed, 46 insertions(+)
>
> diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
> index db213eb7cb02..ce4739e2b407 100644
> --- a/arch/powerpc/perf/hv-24x7.c
> +++ b/arch/powerpc/perf/hv-24x7.c
> @@ -31,6 +31,8 @@ static int interface_version;
> /* Whether we have to aggregate result data for some domains. */
> static bool aggregate_result_elements;
>
> +static cpumask_t hv_24x7_cpumask;
> +
> static bool domain_is_valid(unsigned domain)
> {
> switch (domain) {
> @@ -1641,6 +1643,44 @@ static struct pmu h_24x7_pmu = {
> .capabilities = PERF_PMU_CAP_NO_EXCLUDE,
> };
>
> +static int ppc_hv_24x7_cpu_online(unsigned int cpu)
> +{
> + /* Make this CPU the designated target for counter collection */
The comment implies every newly onlined CPU will become the target, but
actually it's only the first onlined CPU.
So I think the comment needs updating, or you could just drop the
comment, I think the code is fairly clear by itself.
> + if (cpumask_empty(&hv_24x7_cpumask))
> + cpumask_set_cpu(cpu, &hv_24x7_cpumask);
> +
> + return 0;
> +}
> +
> +static int ppc_hv_24x7_cpu_offline(unsigned int cpu)
> +{
> + int target = -1;
No need to initialise target, you assign to it unconditionally below.
> + /* Check if exiting cpu is used for collecting 24x7 events */
> + if (!cpumask_test_and_clear_cpu(cpu, &hv_24x7_cpumask))
> + return 0;
> +
> + /* Find a new cpu to collect 24x7 events */
> + target = cpumask_last(cpu_active_mask);
Any reason to use cpumask_last() vs cpumask_first(), or a randomly
chosen CPU?
> + if (target < 0 || target >= nr_cpu_ids)
> + return -1;
> +
> + /* Migrate 24x7 events to the new target */
> + cpumask_set_cpu(target, &hv_24x7_cpumask);
> + perf_pmu_migrate_context(&h_24x7_pmu, cpu, target);
> +
> + return 0;
> +}
> +
> +static int hv_24x7_cpu_hotplug_init(void)
> +{
> + return cpuhp_setup_state(CPUHP_AP_PERF_POWERPC_HV_24x7_ONLINE,
> + "perf/powerpc/hv_24x7:online",
> + ppc_hv_24x7_cpu_online,
> + ppc_hv_24x7_cpu_offline);
> +}
> +
> static int hv_24x7_init(void)
> {
> int r;
> @@ -1685,6 +1725,11 @@ static int hv_24x7_init(void)
> if (r)
> return r;
>
> + /* init cpuhotplug */
> + r = hv_24x7_cpu_hotplug_init();
> + if (r)
> + pr_err("hv_24x7: CPU hotplug init failed\n");
> +
The hotplug initialisation shouldn't fail unless something is badly
wrong. I think you should just fail initialisation of the entire PMU if
that happens, which will make the error handling in the next patch much
simpler.
cheers
> r = perf_pmu_register(&h_24x7_pmu, h_24x7_pmu.name, -1);
> if (r)
> return r;
next prev parent reply other threads:[~2020-07-06 3:12 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-26 10:28 [PATCH v3 0/2] Add cpu hotplug support for powerpc/perf/hv-24x7 Kajol Jain
2020-06-26 10:28 ` [PATCH v3 1/2] powerpc/perf/hv-24x7: Add cpu hotplug support Kajol Jain
2020-07-06 3:13 ` Michael Ellerman [this message]
2020-07-07 4:15 ` Madhavan Srinivasan
2020-07-07 4:56 ` Michael Ellerman
2020-07-07 5:36 ` Madhavan Srinivasan
2020-07-07 10:59 ` kajoljain
2020-06-26 10:28 ` [PATCH v3 2/2] powerpc/hv-24x7: Add sysfs files inside hv-24x7 device to show cpumask Kajol Jain
2020-07-02 14:36 ` Gautham R Shenoy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87zh8d5oab.fsf@mpe.ellerman.id.au \
--to=mpe@ellerman$(echo .)id.au \
--cc=anju@linux$(echo .)vnet.ibm.com \
--cc=ego@linux$(echo .)vnet.ibm.com \
--cc=kjain@linux$(echo .)ibm.com \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=maddy@linux$(echo .)vnet.ibm.com \
--cc=nathanl@linux$(echo .)ibm.com \
--cc=suka@us$(echo .)ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox