linux-kernel - Re: [PATCH v3 7/7] perf expr: Migrate expr ids table to a hashmap

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Date:   Mon, 18 May 2020 09:29:06 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     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>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Kim Phillips <kim.phillips@....com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Leo Yan <leo.yan@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v3 7/7] perf expr: Migrate expr ids table to a hashmap

On Mon, May 18, 2020 at 9:11 AM Arnaldo Carvalho de Melo
<arnaldo.melo@...il.com> wrote:
>
> Em Mon, May 18, 2020 at 01:06:48PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Em Mon, May 18, 2020 at 09:03:45AM -0700, Ian Rogers escreveu:
> > > On Mon, May 18, 2020 at 8:45 AM Arnaldo Carvalho de Melo wrote:
> > > this build issue sounds like this patch is missing:
> > > https://lore.kernel.org/lkml/20200515221732.44078-3-irogers@google.com/
> > > The commit message there could have explicitly said having this
> > > #include causes the conflicting definitions between perf's debug.h and
> > > libbpf_internal.h's definitions of pr_info, etc.
> >
> > yeah, understood, but I'm not processing patches for tools/lib/bpf/,
> > Daniel is, I'll only get that one later, then we can go back to the way
> > you structured it. Just an extra bit of confusion in this process ;-)
>
> So, thiis is failing on all alpine Linux containers:
>
>   CC       /tmp/build/perf/util/metricgroup.o
>   CC       /tmp/build/perf/util/header.o
> In file included from util/metricgroup.c:25:0:
> /git/linux/tools/lib/api/fs/fs.h:16:0: error: "FS" redefined [-Werror]
>  #define FS(name)    \
>  ^
> In file included from /git/linux/tools/perf/util/hashmap.h:16:0,
>                  from util/expr.h:11,
>                  from util/metricgroup.c:14:
> /usr/include/bits/reg.h:28:0: note: this is the location of the previous definition
>  #define FS     25
>  ^
>   CC       /tmp/build/perf/util/callchain.o
>   CC       /tmp/build/perf/util/values.o
>   CC       /tmp/build/perf/util/debug.o
>   CC       /tmp/build/perf/util/fncache.o
> cc1: all warnings being treated as errors
> mv: can't rename '/tmp/build/perf/util/.metricgroup.o.tmp': No such file or directory
> /git/linux/tools/build/Makefile.build:96: recipe for target '/tmp/build/perf/util/metricgroup.o' failed
>
>
> I'll check that soon,
>
> - Arnaldo

I had some issues here too:
https://lore.kernel.org/lkml/CAEf4BzYxTTND7T7X0dLr2CbkEvUuKtarOeoJYYROefij+qds0w@mail.gmail.com/
The only reason for the bits/reg.h inclusion is for __WORDSIZE for the
hash_bits operation. As shown below:

#ifdef __GLIBC__
#include <bits/wordsize.h>
#else
#include <bits/reg.h>
#endif
static inline size_t hash_bits(size_t h, int bits)
{
/* shuffle bits and return requested number of upper bits */
return (h * 11400714819323198485llu) >> (__WORDSIZE - bits);
}

It'd be possible to change the definition of hash_bits and remove the
#includes by:

static inline size_t hash_bits(size_t h, int bits)
{
/* shuffle bits and return requested number of upper bits */
#ifdef __LP64__
  int shift = 64 - bits;
#else
  int shift = 32 - bits;
#endif
return (h * 11400714819323198485llu) >> shift;
}

Others may have a prefered more portable solution. A separate issue
with this same function is undefined behavior getting flagged
(unnecessarily) by sanitizers:
https://lore.kernel.org/lkml/20200508063954.256593-1-irogers@google.com/

I was planning to come back to that once we got these changes landed.

Thanks!
Ian