Hi.
On 05.12.2019 00:00, Ravi Pokala wrote:
> -----Original Message-----
> From: <[email protected]> on behalf of Alexander Motin
> <[email protected]>
> Date: 2019-12-04, Wednesday at 20:52
> To: <[email protected]>, <[email protected]>,
> <[email protected]>
> Subject: svn commit: r355412 - head/sys/geom
>
> Author: mav
> Date: Thu Dec 5 04:52:19 2019
> New Revision: 355412
> URL: https://svnweb.freebsd.org/changeset/base/355412
>
> Log:
> Wrap g_trace() into a macro to avoid unneeded calls.
>
> In most cases with debug disabled this function does nothing, but
> argument
> passing and the call still cost measurable time due to cache misses,
> etc.
>
> Hi Alexander,
>
> I'm having trouble understanding this change, on a few levels.
>
> - Why did you add parentheses around the function declaration and definition?
To make pre-processor not replace them also.
> - How can that function with that name co-exist with a macro of the same name?
The macro is handled first by pre-processor, compiler goes second on the
result.
> - Isn't the "g_debugflags" test in geom_dump.c:g_trace() now redundant?
> - Why not simply convert geom_dump.c:g_trace() into a 'static inline' in
> geom.h, and not have to bother with the macro at all?
One answer to both questions: compatibility with already built modules
require the function to be present and behave same as before, while
newly built code should be more efficient without changes.
> What am I missing?
>
> Thanks,
>
> Ravi (rpokala@)
>
> MFC after: 2 weeks
> Sponsored by: iXsystems, Inc.
>
> Modified:
> head/sys/geom/geom.h
> head/sys/geom/geom_dump.c
>
> Modified: head/sys/geom/geom.h
>
> ==============================================================================
> --- head/sys/geom/geom.h Thu Dec 5 04:18:22 2019 (r355411)
> +++ head/sys/geom/geom.h Thu Dec 5 04:52:19 2019 (r355412)
> @@ -255,11 +255,15 @@ void g_dev_physpath_changed(void);
> struct g_provider *g_dev_getprovider(struct cdev *dev);
>
> /* geom_dump.c */
> -void g_trace(int level, const char *, ...);
> +void (g_trace)(int level, const char *, ...) __printflike(2, 3);
> # define G_T_TOPOLOGY 1
> # define G_T_BIO 2
> # define G_T_ACCESS 4
> -
> +extern int g_debugflags;
> +#define g_trace(level, fmt, ...) do { \
> + if (__predict_false(g_debugflags & (level))) \
> + (g_trace)(level, fmt, ## __VA_ARGS__); \
> +} while (0)
>
> /* geom_event.c */
> typedef void g_event_t(void *, int flag);
>
> Modified: head/sys/geom/geom_dump.c
>
> ==============================================================================
> --- head/sys/geom/geom_dump.c Thu Dec 5 04:18:22 2019
> (r355411)
> +++ head/sys/geom/geom_dump.c Thu Dec 5 04:52:19 2019
> (r355412)
> @@ -319,7 +319,7 @@ g_confxml(void *p, int flag)
> }
>
> void
> -g_trace(int level, const char *fmt, ...)
> +(g_trace)(int level, const char *fmt, ...)
> {
> va_list ap;
--
Alexander Motin
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