I don't believe so. The issue I'm trying to address is that there is still
significant execution time overhead for debug output calls when
proxy.config.diags.debug.enabled is 0. This change would make the
execution time overhead negligible (if TSFastDbg is used or TSDebug is
changed to be like the proposed TSFastDbg). Another way of putting it is,
I want to clean up the existing TSDEBUG alternative to TSDebug.
On Wed, Jun 12, 2019 at 11:31 AM Bryan Call <bc...@apache.org> wrote:
> How would this be controlled on the command line when running
> trafic_server -T?
>
> It looks like it is a departure from how debug tags and controlled now.
>
> -Bryan
>
>
> > On Jun 11, 2019, at 1:21 PM, Walt Karas <wka...@verizonmedia.com.INVALID>
> wrote:
> >
> > Any +1's for simply replacing TSDebug with the proposed TSFastDbg ?
> >
> > On Mon, Apr 8, 2019 at 6:20 PM Leif Hedstrom <zw...@apache.org> wrote:
> >
> >>
> >>
> >> On Apr 4, 2019, at 8:05 AM, Walt Karas <wka...@verizonmedia.com
> .INVALID>
> >> wrote:
> >>
> >> Because senility. probably "on" should be a non-pointer of type const
> >> volatile char, and InkAPI in the core can just keep a pointer to the
> whole
> >> structure for updating.
> >>
> >> But I'm leaning more to fixing up the capability that already kinda
> there.
> >> Which is optimizimg only for the case when all debug output is disabled.
> >> Especially since maybe zwoop would be on my side for once :o) .
> >>
> >>
> >>
> >> My bad, whatever Walt said, I take the opposite stance.
> >>
> >> — leif
> >>
> >> P.s
> >> J/K!
> >>
> >>
> >> On Thu, Apr 4, 2019 at 8:51 AM Alan Carroll
> >> <solidwallofc...@verizonmedia.com.invalid> wrote:
> >>
> >> This could enable a significant speed up for debug tags. One point is
> that
> >> when the debug tag string is set, at that point the debug objects could
> be
> >> updated to the correct state according to the debug tag string, rather
> than
> >> checking it every time a debug message is logged.
> >>
> >> I have to ask, why is there a pointer to the enable flag, instead of
> just
> >> the enable flag? Your logic doesn't even check that flag, it checks
> whether
> >> the pointer is null.
> >>
> >> On Wed, Apr 3, 2019 at 11:52 AM Leif Hedstrom <zw...@apache.org> wrote:
> >>
> >>
> >>
> >> On Apr 3, 2019, at 10:47 AM, Walt Karas <wka...@verizonmedia.com
> >>
> >> .INVALID>
> >>
> >> wrote:
> >>
> >>
> >> It looks like the TS API already has less granular version of this:
> >>
> >> extern int diags_on_for_plugins;
> >>
> >> #define TSDEBUG \
> >>
> >> if (diags_on_for_plugins) \
> >>
> >> TSDebug
> >>
> >>
> >> A problem with this is if you write:
> >>
> >>
> >> if (flag)
> >>
> >> TSDEBUG(yadayada);
> >>
> >> else
> >>
> >> do_something();
> >>
> >>
> >> then the else will be associated with the if hidden in the macro. I'd
> >> prefer to change to something like:
> >>
> >>
> >> extern const volatile char TS_detail_dbg_output_enabled;
> >>
> >>
> >> #define TSFastDbg(_TAG, ...) \
> >> do { \
> >> if (TS_detail_dbg_output_enabled) \
> >> TSDebug(_TAG, __VA_ARGS__); \
> >>
> >> } while(0)
> >>
> >>
> >> Yeh, that kinda sounds like a bug, doesn’t it?
> >>
> >>
> >> The negative is that we'd only see the benefit when all debug output
> >>
> >> was
> >>
> >> disabled. But, in any case, that is the main benefit, to avoid impacts
> >> during normal operation.
> >>
> >>
> >> Right, we should always optimize for the common cases, obviously. When
> >> there’s a decision to make, where you can either make it “equally”
> >> expensive always, or more expensive in a rare case, but cheaper in the
> >> common case, we should likely chose the latter.
> >>
> >>
> >>
> >>
> >> Looking in src/tscore/Diags.cc, it looks like the debug enable flag is
> >>
> >> only
> >>
> >> set at startup time. So we wouldn't be able to enable TSFastDbg using
> >> traffic_cntl without adding complexity.
> >>
> >> On Tue, Apr 2, 2019 at 5:48 PM Walt Karas <wka...@verizonmedia.com>
> >>
> >> wrote:
> >>
> >>
> >> Add this new structure to apidefs.h:
> >>
> >> typedef struct TSFastDbgCntl_
> >> {
> >> const char * const tag; // nul-terminated string
> >> const volatile char * const on; // pointer to 1-byte flag
> >> }
> >> TSFastDbgCntl;
> >>
> >> Add this new API function, that returns a pointer to an instance of
> >>
> >> the
> >>
> >> above structure:
> >>
> >> TSFastDbgCntl * TSCreateFastDbgCntl(const char *tag);
> >>
> >> Add this macro, which would be used in place of direct use of
> >>
> >> TSDebug().
> >>
> >>
> >> #define TSFastDbg(_FD_CNTL, ...) \
> >> do { \
> >> if ((_FD_CNTL)->on) \
> >> TSDebug((_FD_CNTL)->tag, __VA_ARGS__); \
> >> } while(0)
> >>
> >> The first parameter to TSFastDbg() is a pointer that was returned by
> >> TSCreateFastDbgCntl(). The remaining parameters are printf parameters
> >> (format string and values matching format specifiers). The core would
> >>
> >> be
> >>
> >> responsible for changing the value of the 'on' fields in the
> >>
> >> TSFastDbgCntl
> >>
> >> instances. For direct calls to TSDebug(), even if the tag is
> >>
> >> disabled,
> >>
> >> all
> >>
> >> the parameters have to be prepared and pushed onto the stack. As was
> >> discussed in IRC, you have to feel guilty about doing converting a
> >> string_view to a string and outputting it with c_str(). Because the
> >>
> >> code
> >>
> >> to do this will be executed even if the debug tag is disabled.
> >> Furthermore, for each call to TSDebug, it's necessary to do an
> >>
> >> associative
> >>
> >> lookup on the tag string to determine that output for the tag is
> >>
> >> disabled.
> >>
> >>
> >> We would want to put equivalent capabilities in Diags.h in the core
> >>
> >> for
> >>
> >> debug output. The implementation is non-trivial, but I think it would
> >>
> >> take
> >>
> >> at most a week including the Au test additions.
> >>
> >> I looked at making TSFastDbg() an inline function rather than a macro:
> >> https://godbolt.org/z/IfVbBk
> >> The opitimization works well if you compile the code with the inline
> >> function as C, but the optimization is poor if you compile it as C++.
> >>
> >> This
> >>
> >> difference exists for both gcc and clang. It's weird.
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
>
>
