Messages in this thread | | | Date | Tue, 26 Apr 2022 16:53:13 -0700 | From | "Luck, Tony" <> | Subject | Re: [PATCH v4 09/10] trace: platform/x86/intel/ifs: Add trace point to track Intel IFS operations |
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On Mon, Apr 25, 2022 at 09:49:28PM -0400, Steven Rostedt wrote: > On Mon, 25 Apr 2022 16:49:35 +0000 > "Luck, Tony" <tony.luck@intel.com> wrote: > > > I see two paths: > > > > 1) Create a new user friendly trace point for each new scan mode. > > 2) Just provide a generic one that dumps both the 64-bit WRMSR and RDMSR values. > > > > Q: Are trace points "expensive" in some way ... so better to just have one than three? > > Or are the cheap enough that decoding for the user is an OK thing? > > Yes, they are expensive as each TRACE_EVENT() can add a few KB of text and > data. But you can add a DECLARE_EVENT_CLASS() and then add "printk" > differences that are less memory heavy. > > See DEFINE_EVENT_PRINT().
I looked at the examples in samples/trace_events/trace-events-sample.h and tried to use this. But I'm doing something wrong because the compiler barfs on something defined but not used.
Maybe my problem is the TP_printk() in the DECLARE_EVENT_CLASS() that is over-ridden by DEFINE_EVENT_PRINT(). I wasn't at all sure what to put here ... or how to use the base tracepoint that doesn't have the printk() over-ridden.
I think I need my class to just save both the u64 values to the trace buffer. Then the different trace points will extract the bits they want and print in a user friendly way. While this increases space used in the trace buffer, these events are not crazy high frequency. Usually one or two events per core with a gap 30 minutes or more between tests.
In my ".c" file the tracepoint looks like this using the name from DEFINE_EVENT_PRINT(), and now passing the full u64 values:
trace_ifs_status_saf(activate.data, status.data);
and my #include file looks like this:
---------------------------------------------- /* SPDX-License-Identifier: GPL-2.0 */ #undef TRACE_SYSTEM #define TRACE_SYSTEM intel_ifs
#if !defined(_TRACE_IFS_H) || defined(TRACE_HEADER_MULTI_READ) #define _TRACE_IFS_H
#include <linux/ktime.h> #include <linux/tracepoint.h>
DECLARE_EVENT_CLASS(ifs_status,
TP_PROTO(u64 activate, u64 status),
TP_ARGS(activate, status),
TP_STRUCT__entry( __field( u64, activate ) __field( u64, status ) ),
TP_fast_assign( __entry->activate = activate; __entry->status = status; ),
TP_printk("activate: %llx status: %llx", __entry->activate, __entry->status) );
DEFINE_EVENT_PRINT(ifs_status, ifs_status_saf, TP_PROTO(u64 activate, u64 status), TP_ARGS(activate, status), TP_printk("start: %.2x, stop: %.2x, status: %llx", ((union ifs_scan *)&(__entry->activate))->start, ((union ifs_scan *)&(__entry->activate))->stop, __entry->status) );
#endif /* _TRACE_IFS_H */
/* This part must be outside protection */ #include <trace/define_trace.h> -----------------------------------------------------
GCC messages:
CC [M] drivers/platform/x86/intel/ifs/runtest.o In file included from /home/agluck/GIT/mywork/include/trace/define_trace.h:102, from /home/agluck/GIT/mywork/include/trace/events/intel_ifs.h:44, from /home/agluck/GIT/mywork/drivers/platform/x86/intel/ifs/runtest.c:27: /home/agluck/GIT/mywork/include/trace/trace_events.h:426:13: warning: ‘print_fmt_ifs_status’ defined but not used [-Wunused-variable] 426 | static char print_fmt_##call[] = print; \ | ^~~~~~~~~~ /home/agluck/GIT/mywork/include/trace/events/intel_ifs.h:11:1: note: in expansion of macro ‘DECLARE_EVENT_CLASS’ 11 | DECLARE_EVENT_CLASS(ifs_status, | ^~~~~~~~~~~~~~~~~~~ In file included from /home/agluck/GIT/mywork/include/trace/define_trace.h:102, from /home/agluck/GIT/mywork/include/trace/events/intel_ifs.h:44, from /home/agluck/GIT/mywork/drivers/platform/x86/intel/ifs/runtest.c:27: /home/agluck/GIT/mywork/include/trace/trace_events.h:207:37: warning: ‘trace_event_type_funcs_ifs_status’ defined but not used [-Wunused-variable] 207 | static struct trace_event_functions trace_event_type_funcs_##call = { \ | ^~~~~~~~~~~~~~~~~~~~~~~ /home/agluck/GIT/mywork/include/trace/events/intel_ifs.h:11:1: note: in expansion of macro ‘DECLARE_EVENT_CLASS’ 11 | DECLARE_EVENT_CLASS(ifs_status, | ^~~~~~~~~~~~~~~~~~~ make[1]: Leaving directory '/home/agluck/GIT/mywork/build/ifsv5-rc1'
-Tony
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