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Subject: Re: [PATCH 3/3] SUNRPC: Count ops completing with tk_status < 0
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <f7976bde9979e8b763c0009b523331ab5ce6b6ed.camel@redhat.com>
Date:   Mon, 3 Jun 2019 14:56:29 -0400
Cc:     Bruce Fields <bfields@fieldses.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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References: <20190523201351.12232-1-dwysocha@redhat.com>
 <20190523201351.12232-3-dwysocha@redhat.com>
 <20190530213857.GA24802@fieldses.org>
 <9B9F0C9B-C493-44F5-ABD1-6B2B4BAA2F08@oracle.com>
 <20190530223314.GA25368@fieldses.org>
 <CD3B0503-ABA0-4670-9A76-0B9DF0AE5B5C@oracle.com>
 <f7976bde9979e8b763c0009b523331ab5ce6b6ed.camel@redhat.com>
To:     Dave Wysochanski <dwysocha@redhat.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Jun 3, 2019, at 2:53 PM, Dave Wysochanski <dwysocha@redhat.com> wrote:
> 
> On Fri, 2019-05-31 at 09:25 -0400, Chuck Lever wrote:
>>> On May 30, 2019, at 6:33 PM, Bruce Fields <bfields@fieldses.org>
>>> wrote:
>>> 
>>> On Thu, May 30, 2019 at 06:19:54PM -0400, Chuck Lever wrote:
>>>> 
>>>> 
>>>>> On May 30, 2019, at 5:38 PM, bfields@fieldses.org wrote:
>>>>> 
>>>>> On Thu, May 23, 2019 at 04:13:50PM -0400, Dave Wysochanski
>>>>> wrote:
>>>>>> We often see various error conditions with NFS4.x that show
>>>>>> up with
>>>>>> a very high operation count all completing with tk_status < 0
>>>>>> in a
>>>>>> short period of time.  Add a count to rpc_iostats to record
>>>>>> on a
>>>>>> per-op basis the ops that complete in this manner, which will
>>>>>> enable lower overhead diagnostics.
>>>>> 
>>>>> Looks like a good idea to me.
>>>>> 
>>>>> It's too bad we can't distinguish the errors.  (E.g. ESTALE on
>>>>> a lookup
>>>>> call is a lot more interesting than ENOENT.)  But understood
>>>>> that
>>>>> maintaining (number of possible errors) * (number of possible
>>>>> ops)
>>>>> counters is probably overkill, so just counting the number of
>>>>> errors
>>>>> seems like a good start.
>>>> 
>>>> We now have trace points that can do that too.
>>> 
>>> You mean, that can report every error (and its value)?
>> 
>> Yes, the nfs_xdr_status trace point reports the error by value and
>> symbolic name.
>> 
> 
> The tracepoint is very useful I agree.  I don't think it will show:
> a) the mount
> b) the opcode
> 
> Or am I mistaken and there's a way to get those with a filter or
> another tracepoint?

The opcode can be exposed by another trace point, but the link between
the two trace points is tenuous and could be improved.

I don't believe any of the NFS trace points expose the mount. My testing
is largely on a single mount so my imagination stopped there.


>>> I assume having these statistics in mountstats is still useful,
>>> though.
>>> 
>>> --b.
>>> 
>>>> 
>>>> 
>>>>> --b.
>>>>> 
>>>>>> 
>>>>>> Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
>>>>>> ---
>>>>>> include/linux/sunrpc/metrics.h | 7 ++++++-
>>>>>> net/sunrpc/stats.c             | 8 ++++++--
>>>>>> 2 files changed, 12 insertions(+), 3 deletions(-)
>>>>>> 
>>>>>> diff --git a/include/linux/sunrpc/metrics.h
>>>>>> b/include/linux/sunrpc/metrics.h
>>>>>> index 1b3751327575..0ee3f7052846 100644
>>>>>> --- a/include/linux/sunrpc/metrics.h
>>>>>> +++ b/include/linux/sunrpc/metrics.h
>>>>>> @@ -30,7 +30,7 @@
>>>>>> #include <linux/ktime.h>
>>>>>> #include <linux/spinlock.h>
>>>>>> 
>>>>>> -#define RPC_IOSTATS_VERS	"1.0"
>>>>>> +#define RPC_IOSTATS_VERS	"1.1"
>>>>>> 
>>>>>> struct rpc_iostats {
>>>>>> 	spinlock_t		om_lock;
>>>>>> @@ -66,6 +66,11 @@ struct rpc_iostats {
>>>>>> 	ktime_t			om_queue,	/* queued for
>>>>>> xmit */
>>>>>> 				om_rtt,		/* RPC RTT */
>>>>>> 				om_execute;	/* RPC
>>>>>> execution */
>>>>>> +	/*
>>>>>> +	 * The count of operations that complete with tk_status
>>>>>> < 0.
>>>>>> +	 * These statuses usually indicate error conditions.
>>>>>> +	 */
>>>>>> +	unsigned long           om_error_status;
>>>>>> } ____cacheline_aligned;
>>>>>> 
>>>>>> struct rpc_task;
>>>>>> diff --git a/net/sunrpc/stats.c b/net/sunrpc/stats.c
>>>>>> index 8b2d3c58ffae..737414247ca7 100644
>>>>>> --- a/net/sunrpc/stats.c
>>>>>> +++ b/net/sunrpc/stats.c
>>>>>> @@ -176,6 +176,8 @@ void rpc_count_iostats_metrics(const
>>>>>> struct rpc_task *task,
>>>>>> 
>>>>>> 	execute = ktime_sub(now, task->tk_start);
>>>>>> 	op_metrics->om_execute = ktime_add(op_metrics-
>>>>>>> om_execute, execute);
>>>>>> +	if (task->tk_status < 0)
>>>>>> +		op_metrics->om_error_status++;
>>>>>> 
>>>>>> 	spin_unlock(&op_metrics->om_lock);
>>>>>> 
>>>>>> @@ -218,13 +220,14 @@ static void _add_rpc_iostats(struct
>>>>>> rpc_iostats *a, struct rpc_iostats *b)
>>>>>> 	a->om_queue = ktime_add(a->om_queue, b->om_queue);
>>>>>> 	a->om_rtt = ktime_add(a->om_rtt, b->om_rtt);
>>>>>> 	a->om_execute = ktime_add(a->om_execute, b-
>>>>>>> om_execute);
>>>>>> +	a->om_error_status += b->om_error_status;
>>>>>> }
>>>>>> 
>>>>>> static void _print_rpc_iostats(struct seq_file *seq, struct
>>>>>> rpc_iostats *stats,
>>>>>> 			       int op, const struct
>>>>>> rpc_procinfo *procs)
>>>>>> {
>>>>>> 	_print_name(seq, op, procs);
>>>>>> -	seq_printf(seq, "%lu %lu %lu %llu %llu %llu %llu
>>>>>> %llu\n",
>>>>>> +	seq_printf(seq, "%lu %lu %lu %llu %llu %llu %llu %llu
>>>>>> %lu\n",
>>>>>> 		   stats->om_ops,
>>>>>> 		   stats->om_ntrans,
>>>>>> 		   stats->om_timeouts,
>>>>>> @@ -232,7 +235,8 @@ static void _print_rpc_iostats(struct
>>>>>> seq_file *seq, struct rpc_iostats *stats,
>>>>>> 		   stats->om_bytes_recv,
>>>>>> 		   ktime_to_ms(stats->om_queue),
>>>>>> 		   ktime_to_ms(stats->om_rtt),
>>>>>> -		   ktime_to_ms(stats->om_execute));
>>>>>> +		   ktime_to_ms(stats->om_execute),
>>>>>> +		   stats->om_error_status);
>>>>>> }
>>>>>> 
>>>>>> void rpc_clnt_show_stats(struct seq_file *seq, struct
>>>>>> rpc_clnt *clnt)
>>>>>> -- 
>>>>>> 2.20.1
>>>> 
>>>> --
>>>> Chuck Lever
>> 
>> --
>> Chuck Lever

--
Chuck Lever