> On May 4, 2020, at 12:04 PM, bfields@xxxxxxxxxxxx wrote:
>
> On Fri, May 01, 2020 at 01:22:27PM -0400, Chuck Lever wrote:
>> - Rename these so they are easy to enable and search for as a set
>> - Move the tracepoints to get a more accurate sense of control flow
>> - Tracepoints should not fire on xprt shutdown
>> - Display memory address in case data structure had been corrupted
>> - Abandon dprintk in these paths
>>
>> I haven't ever gotten one of these tracepoints to trigger. I wonder
>> if we should simply remove them.
>
> It's definitely not dead code.
Sure. I'm just suggesting that maybe we could make do with just a single
tracepoint here (or maybe, no tracepoints) since these paths don't seem
to trigger often.
> But I forget the conditions required to
> hit those cases. Looking.... So, we in cache_check we have a cache miss
> that requires an upcall, and call cache_defer_req, which will wait for a
> response 1 or 5 seconds (depending on how busy server threads are) and
> then calls svc_defer().
It would be valuable to have some stock test cases in our community tools
that would exercise these paths.
> --b.
>
>>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> include/trace/events/sunrpc.h | 11 ++++++++---
>> net/sunrpc/svc_xprt.c | 12 ++++++------
>> 2 files changed, 14 insertions(+), 9 deletions(-)
>>
>> diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
>> index ffd2215950dc..3158b3f7e01e 100644
>> --- a/include/trace/events/sunrpc.h
>> +++ b/include/trace/events/sunrpc.h
>> @@ -1313,27 +1313,32 @@ DECLARE_EVENT_CLASS(svc_deferred_event,
>> TP_ARGS(dr),
>>
>> TP_STRUCT__entry(
>> + __field(const void *, dr)
>> __field(u32, xid)
>> __string(addr, dr->xprt->xpt_remotebuf)
>> ),
>>
>> TP_fast_assign(
>> + __entry->dr = dr;
>> __entry->xid = be32_to_cpu(*(__be32 *)(dr->args +
>> (dr->xprt_hlen>>2)));
>> __assign_str(addr, dr->xprt->xpt_remotebuf);
>> ),
>>
>> - TP_printk("addr=%s xid=0x%08x", __get_str(addr), __entry->xid)
>> + TP_printk("addr=%s dr=%p xid=0x%08x", __get_str(addr), __entry->dr,
>> + __entry->xid)
>> );
>> +
>> #define DEFINE_SVC_DEFERRED_EVENT(name) \
>> - DEFINE_EVENT(svc_deferred_event, svc_##name##_deferred, \
>> + DEFINE_EVENT(svc_deferred_event, svc_defer_##name, \
>> TP_PROTO( \
>> const struct svc_deferred_req *dr \
>> ), \
>> TP_ARGS(dr))
>>
>> DEFINE_SVC_DEFERRED_EVENT(drop);
>> -DEFINE_SVC_DEFERRED_EVENT(revisit);
>> +DEFINE_SVC_DEFERRED_EVENT(queue);
>> +DEFINE_SVC_DEFERRED_EVENT(recv);
>>
>> DECLARE_EVENT_CLASS(cache_event,
>> TP_PROTO(
>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
>> index 2284ff038dad..e12ec68cd0ff 100644
>> --- a/net/sunrpc/svc_xprt.c
>> +++ b/net/sunrpc/svc_xprt.c
>> @@ -1158,16 +1158,15 @@ static void svc_revisit(struct cache_deferred_req *dreq, int too_many)
>> set_bit(XPT_DEFERRED, &xprt->xpt_flags);
>> if (too_many || test_bit(XPT_DEAD, &xprt->xpt_flags)) {
>> spin_unlock(&xprt->xpt_lock);
>> - dprintk("revisit canceled\n");
>> + trace_svc_defer_drop(dr);
>> svc_xprt_put(xprt);
>> - trace_svc_drop_deferred(dr);
>> kfree(dr);
>> return;
>> }
>> - dprintk("revisit queued\n");
>> dr->xprt = NULL;
>> list_add(&dr->handle.recent, &xprt->xpt_deferred);
>> spin_unlock(&xprt->xpt_lock);
>> + trace_svc_defer_queue(dr);
>> svc_xprt_enqueue(xprt);
>> svc_xprt_put(xprt);
>> }
>> @@ -1213,22 +1212,24 @@ static struct cache_deferred_req *svc_defer(struct cache_req *req)
>> memcpy(dr->args, rqstp->rq_arg.head[0].iov_base - skip,
>> dr->argslen << 2);
>> }
>> + trace_svc_defer(rqstp);
>> svc_xprt_get(rqstp->rq_xprt);
>> dr->xprt = rqstp->rq_xprt;
>> set_bit(RQ_DROPME, &rqstp->rq_flags);
>>
>> dr->handle.revisit = svc_revisit;
>> - trace_svc_defer(rqstp);
>> return &dr->handle;
>> }
>>
>> /*
>> * recv data from a deferred request into an active one
>> */
>> -static int svc_deferred_recv(struct svc_rqst *rqstp)
>> +static noinline int svc_deferred_recv(struct svc_rqst *rqstp)
>> {
>> struct svc_deferred_req *dr = rqstp->rq_deferred;
>>
>> + trace_svc_defer_recv(dr);
>> +
>> /* setup iov_base past transport header */
>> rqstp->rq_arg.head[0].iov_base = dr->args + (dr->xprt_hlen>>2);
>> /* The iov_len does not include the transport header bytes */
>> @@ -1259,7 +1260,6 @@ static struct svc_deferred_req *svc_deferred_dequeue(struct svc_xprt *xprt)
>> struct svc_deferred_req,
>> handle.recent);
>> list_del_init(&dr->handle.recent);
>> - trace_svc_revisit_deferred(dr);
>> } else
>> clear_bit(XPT_DEFERRED, &xprt->xpt_flags);
>> spin_unlock(&xprt->xpt_lock);
--
Chuck Lever
