Messages in this thread | | | Subject | Re: [PATCH] tracing: fix "gfp_t" format for synthetic events | From | Tom Zanussi <> | Date | Thu, 17 Oct 2019 09:27:06 -0500 |
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Hi Zhengjun,
On Thu, 2019-10-17 at 16:38 +0800, Zhengjun Xing wrote: > In the format of synthetic events, the "gfp_t" is shown as > "signed:1", > but in fact the "gfp_t" is "unsigned", should be shown as "signed:0". > The offset should be increased by the real size of each field, rather > than by the size of "u64". > > The issue can be reproduced by the following commands: > > echo 'memlatency u64 lat; unsigned int order; gfp_t gfp_flags; int > migratetype' > /sys/kernel/debug/tracing/synthetic_events > cat /sys/kernel/debug/tracing/events/synthetic/memlatency/format > > name: memlatency > ID: 2233 > format: > field:unsigned short > common_type; offset:0; size:2; signed:0; > field:unsigned char > common_flags; offset:2; size:1; signed:0; > field:unsigned char > common_preempt_count; offset:3; size:1; signed:0; > field:int common_pid; offset:4; size:4; signed:1; > > field:u64 lat; offset:8; size:8; signed:0; > field:unsigned int order; offset:16; size:4; > signed:0; > field:gfp_t gfp_flags; offset:24; size:4; signed:1; > field:int migratetype; offset:32; size:4; signed:1; > > print fmt: "lat=%llu, order=%u, gfp_flags=%x, migratetype=%d", REC- > >lat, REC->order, REC->gfp_flags, REC->migratetype > > Signed-off-by: Zhengjun Xing <zhengjun.xing@linux.intel.com> > --- > kernel/trace/trace_events_hist.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_events_hist.c > b/kernel/trace/trace_events_hist.c > index 57648c5aa679..7d70321d03b1 100644 > --- a/kernel/trace/trace_events_hist.c > +++ b/kernel/trace/trace_events_hist.c > @@ -665,7 +665,7 @@ static int synth_event_define_fields(struct > trace_event_call *call) > offset += STR_VAR_LEN_MAX; > n_u64 += STR_VAR_LEN_MAX / sizeof(u64); > } else { > - offset += sizeof(u64); > + offset += size; > n_u64++; > } > }
This part isn't correct - currently, all the synthetic event fields are u64, so doing this alone will mess things up. The synthetic fields were defined to be u64 in order to simplify event generation - if we want to use the actual sizes, it would take a more extensive patch including the generation code as well. Not sure the added complexity is worth it to save a few bytes in the ring buffer.
> @@ -679,6 +679,8 @@ static bool synth_field_signed(char *type) > { > if (str_has_prefix(type, "u")) > return false; > + if (strcmp(type, "gfp_t") == 0) > + return false; > > return true; > }
This part is fine and makes sense.
Thanks,
Tom
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