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    SubjectRe: [PATCH v4 09/10] trace: platform/x86/intel/ifs: Add trace point to track Intel IFS operations
    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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