linux-kernel - [PATCH v2] fpga: dfl: fme: Fix cpu hotplug issue in performance reporting

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Message-Id: <20210709084319.33776-1-kjain@linux.ibm.com>
Date:   Fri,  9 Jul 2021 14:13:19 +0530
From:   Kajol Jain <kjain@...ux.ibm.com>
To:     will@...nel.org, hao.wu@...el.com, mark.rutland@....com
Cc:     trix@...hat.com, yilun.xu@...el.com, mdf@...nel.org,
        linux-fpga@...r.kernel.org, maddy@...ux.ibm.com,
        atrajeev@...ux.vnet.ibm.com, kjain@...ux.ibm.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        rnsastry@...ux.ibm.com, linux-perf-users@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH v2] fpga: dfl: fme: Fix cpu hotplug issue in performance reporting

The performance reporting driver added cpu hotplug
feature but it didn't add pmu migration call in cpu
offline function.
This can create an issue incase the current designated
cpu being used to collect fme pmu data got offline,
as based on current code we are not migrating fme pmu to
new target cpu. Because of that perf will still try to
fetch data from that offline cpu and hence we will not
get counter data.

Patch fixed this issue by adding pmu_migrate_context call
in fme_perf_offline_cpu function.

Fixes: 724142f8c42a ("fpga: dfl: fme: add performance reporting support")
Tested-by: Xu Yilun <yilun.xu@...el.com>
Signed-off-by: Kajol Jain <kjain@...ux.ibm.com>
Cc: stable@...r.kernel.org
---
 drivers/fpga/dfl-fme-perf.c | 4 ++++
 1 file changed, 4 insertions(+)

---
Changelog:
v1 -> v2:
- Add stable@...r.kernel.org in cc list

RFC -> PATCH v1
- Remove RFC tag
- Did nits changes on subject and commit message as suggested by Xu Yilun
- Added Tested-by tag
- Link to rfc patch: https://lkml.org/lkml/2021/6/28/112
---
diff --git a/drivers/fpga/dfl-fme-perf.c b/drivers/fpga/dfl-fme-perf.c
index 4299145ef347..b9a54583e505 100644
--- a/drivers/fpga/dfl-fme-perf.c
+++ b/drivers/fpga/dfl-fme-perf.c
@@ -953,6 +953,10 @@ static int fme_perf_offline_cpu(unsigned int cpu, struct hlist_node *node)
 		return 0;
 
 	priv->cpu = target;
+
+	/* Migrate fme_perf pmu events to the new target cpu */
+	perf_pmu_migrate_context(&priv->pmu, cpu, target);
+
 	return 0;
 }
 
-- 
2.31.1