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Tue, 7 Jul 2020 04:15:40 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7A59EA4057; Tue, 7 Jul 2020 04:15:38 +0000 (GMT) Received: from [9.199.54.78] (unknown [9.199.54.78]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Tue, 7 Jul 2020 04:15:38 +0000 (GMT) Subject: Re: [PATCH v3 1/2] powerpc/perf/hv-24x7: Add cpu hotplug support To: Michael Ellerman , Kajol Jain , linuxppc-dev@lists.ozlabs.org References: <20200626102824.270923-1-kjain@linux.ibm.com> <20200626102824.270923-2-kjain@linux.ibm.com> <87zh8d5oab.fsf@mpe.ellerman.id.au> From: Madhavan Srinivasan Message-ID: <3b45d050-c27a-e5e7-8649-924910f5b01b@linux.ibm.com> Date: Tue, 7 Jul 2020 09:45:37 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <87zh8d5oab.fsf@mpe.ellerman.id.au> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-07_01:2020-07-06, 2020-07-06 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 adultscore=0 priorityscore=1501 lowpriorityscore=0 phishscore=0 mlxlogscore=999 impostorscore=0 malwarescore=0 clxscore=1015 spamscore=0 cotscore=-2147483648 suspectscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2007070025 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: nathanl@linux.ibm.com, ego@linux.vnet.ibm.com, suka@us.ibm.com, maddy@linux.vnet.ibm.com, anju@linux.vnet.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 7/6/20 8:43 AM, Michael Ellerman wrote: > Kajol Jain 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 >> Reviewed-by: Gautham R. Shenoy >> --- >> 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. We  did fail the PMU registration on failure of the hotplug code (and yes error handling is much simpler), but on internal review/discussion, what came up was that, hv_24x7 PMU will still be usable without the hotplug code (with "-C" option to perf tool command line). Maddy > > cheers > >> r = perf_pmu_register(&h_24x7_pmu, h_24x7_pmu.name, -1); >> if (r) >> return r;