Re: Observing Softlockup's while running heavy IOs

[Bart Van Assche <Bart.VanAssche@sandisk.com>]

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On 08/17/16 22:55, Sreekanth Reddy wrote:
> Observing softlockups while running heavy IOs on 8 SSD drives
> connected behind our LSI SAS 3004 HBA.

Hello Sreekanth,

This means that more than 23s was spent before the scheduler was 
invoked, probably due to a loop. Can you give the attached (untested) 
patch a try to see whether it is the loop in __blk_mq_run_hw_queue()?

Thanks,

Bart.


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From 4da94f2ec37ee5d1b4a5f1ce2886bdafd5cd394c Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Thu, 18 Aug 2016 07:51:49 -0700
Subject: [PATCH] block: Measure __blk_mq_run_hw_queue() execution time

Note: the "max_elapsed" variable can be modified by multiple threads
concurrently.
---
 block/blk-mq.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e931a0e..6d0961c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -792,6 +792,9 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 	LIST_HEAD(driver_list);
 	struct list_head *dptr;
 	int queued;
+	static long max_elapsed = -1;
+	unsigned long start = jiffies;
+	long elapsed;
 
 	WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));
 
@@ -889,6 +892,13 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 		 **/
 		blk_mq_run_hw_queue(hctx, true);
 	}
+
+	elapsed = jiffies - start;
+	if (elapsed > max_elapsed) {
+		max_elapsed = elapsed;
+		pr_info("%s() finished after %d ms\n", __func__,
+			jiffies_to_msecs(elapsed));
+	}
 }
 
 /*
-- 
2.9.2