linux-kernel - Re: [PATCH v4 10/11] perf env: Set flag for kernel is 64-bit mode

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Date:   Wed, 14 Jul 2021 11:00:44 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Hunter, Adrian" <adrian.hunter@...el.com>
Cc:     Leo Yan <leo.yan@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 10/11] perf env: Set flag for kernel is 64-bit mode

Em Wed, Jul 14, 2021 at 10:59:49AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Jul 13, 2021 at 05:31:03PM +0000, Hunter, Adrian escreveu:
> > > On Mon, Jul 12, 2021 at 03:14:35PM -0300, Arnaldo Carvalho de Melo wrote:
> > > > Em Sun, Jul 11, 2021 at 06:41:04PM +0800, Leo Yan escreveu:
> > > > > +++ b/tools/perf/util/env.c
> > > > > @@ -11,6 +11,7 @@
> > > > >  #include <stdlib.h>
> > > > >  #include <string.h>
> 
> > > > > +int kernel_is_64_bit;
> > > > >  struct perf_env perf_env;
> 
> > > > Why can't this be in 'struct perf_env'?
> 
> > > Good question.  I considered to add it in struct perf_env but finally I used this
> > > way; the reason is this variable "kernel_is_64_bit" is only used during
> > > recording phase for AUX ring buffer, and don't use it for report.  So seems to
> > > me it's over complexity to add a new field and just wander if it's necessary to
> > > save this field as new feature in the perf header.
> 
> > I think we store the arch, so if the "kernel_is_64_bit" calculation depends only on arch
> > then I guess we don't need a new feature at the moment.
> 
> So, I wasn't suggesting to add this info to the perf.data file header,
> just to the in-memory 'struct perf_env'.
> 
> And also we should avoid unconditionally initializing things that we may
> never need, please structure it as:

Oops, forgot these:
 
> static void perf_env__init_kernel_mode(struct perf_env *env)
> {
>        const char *arch = perf_env__raw_arch(env);
> 
>        if (!strncmp(arch, "x86_64", 6)   || !strncmp(arch, "aarch64", 7) ||
>            !strncmp(arch, "arm64", 5)    || !strncmp(arch, "mips64", 6) ||
>            !strncmp(arch, "parisc64", 8) || !strncmp(arch, "riscv64", 7) ||
>            !strncmp(arch, "s390x", 5)    || !strncmp(arch, "sparc64", 7))
>                kernel_is_64_bit = 1;
                 env->kernel_is_64_bit = 1;
>        else
>                kernel_is_64_bit = 0;
                 env->kernel_is_64_bit = 0;
> }
> 
> 
> void perf_env__init(struct perf_env *env)
> {
> 	...
> 	env->kernel_is_64_bit = -1;
> 	...
> }
> 
> bool perf_env__kernel_is_64_bit(struct perf_env *env)
> {
> 	if (env->kernel_is_64_bit == -1)
> 		perf_env__init_kernel_mode(env);
> 
> 	return env->kernel_is_64_bit;
> }
> 
> One thing in my TODO is to crack down on the tons of initializations
> perf does unconditionally, last time I looked there are lots :-\
> 
> - Arnaldo
>  
> > > Combining the comment from Adrian in another email, I think it's good to add
> > > a new field "compat_mode" in the struct perf_env, and this field will be
> > > initialized in build-record.c.  Currently we don't need to save this value into
> > > the perf file, if later we need to use this value for decoding phase, then we
> > > can add a new feature item to save "compat_mode"
> > > into the perf file's header.
> 
> > > If you have any different idea, please let me know.  Thanks!

-- 

- Arnaldo