Re: [PATCH 04/13] perf env: Introduce read_cpu_topology_map() method

[Namhyung Kim]

Hi Arnaldo,

On Fri, Sep 11, 2015 at 12:33:23PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Fri, Sep 11, 2015 at 11:40:28AM -0300, Arnaldo Carvalho de Melo escreveu:
> > So this is a problem before and after my patches, i.e. If I go on and
> > do, with what we have in acme/perf/core, i.e. none of the changes I'm
> > playing with in perf/env:
> > 
> >   $ git remote update acme
> >   Fetching acme
> >   $ git checkout -b tmp acme/perf/core
> >   Branch tmp set up to track remote branch perf/core from acme.
> >   Switched to a new branch 'tmp'
> >   $ git log --oneline | head -5
> >   7e150fb33a91 perf tests: Introduce iterator function for tests
> >   1765d9b26f84 perf test: Add entry for hists socket filter
> >   207bb55e9193 perf hists browser: Zoom in/out for processor socket
> >   9a2843a5f421 perf report: Introduce --socket-filter option
> >   99851c76436a perf tools: Introduce new sort type "socket" for the processor socket
> >   $ rm -rf /tmp/build/perf ; mkdir -p /tmp/build/perf ; make DEBUG=1 -C tools/perf O=/tmp/build/perf install-bin
> >   # echo 0 > /sys/devices/system/cpu/cpu2/online
> >   $ cat /sys/devices/system/cpu/cpu2/topology/core_id
> >   cat: /sys/devices/system/cpu/cpu2/topology/core_id: No such file or directory
> >   $ ls -la /sys/devices/system/cpu/cpu2/topology/
> >   ls: cannot access /sys/devices/system/cpu/cpu2/topology/: No such file or directory
> >   $ perf record usleep 1
> >   [ perf record: Woken up 1 times to write data ]
> >   [ perf record: Captured and wrote 0.012 MB perf.data (7 samples) ]
> >   [acme@felicio linux]$ perf report --header-only -I 
> >   # ========
> >   # captured on: Fri Sep 11 11:34:18 2015
> >   # hostname : felicio.ghostprotocols.net
> >   # os release : 4.2.0
> >   # perf version : 4.2.g7e150f
> >   #  arch : x86_64
> >   # nrcpus online : 4
> >   # nrcpus avail : 3
> >   # cpudesc : Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz
> >   <SNIP>
> >   # node0 meminfo  : total = 8085412 kB, free = 5317596 kB
> >   # node0 cpu list : 0-1,3
> >   <SNIP>
> >   $ 
> 
> Stephane, Namhyung, the bug report below is about the online/avail
> above, they are swapped, full explanation below.
>  
> > We can see multiple bugs here, right? online/avail is swapped, and when
> > online != avail we simply do not record the cpu topology info at all!
>  
> > If we get that CPU back online:
> > 
> >   # echo 1 > /sys/devices/system/cpu/cpu2/online
> > 
> > Then all works:
> > 
> >   $ perf record usleep 1
> >   [ perf record: Woken up 1 times to write data ]
> >   [ perf record: Captured and wrote 0.012 MB perf.data (7 samples) ]
> >   $ perf report --header-only -I
> >   # ========
> >   # captured on: Fri Sep 11 11:37:31 2015
> >   # hostname : felicio.ghostprotocols.net
> >   # os release : 4.2.0
> >   # perf version : 4.2.g7e150f
> >   # arch : x86_64
> >   # nrcpus online : 4
> >   # nrcpus avail : 4
> >   # cpudesc : Intel(R) Core(TM) i5-2400 CPU @ 3.10GHz
> >   <SNIP>
> >   # sibling cores   : 0-3
> >   # sibling threads : 0
> >   # sibling threads : 1
> >   # sibling threads : 2
> >   # sibling threads : 3
> >   # CPU 0: Core ID 0, Socket ID 0
> >   # CPU 1: Core ID 1, Socket ID 0
> >   # CPU 2: Core ID 2, Socket ID 0
> >   # CPU 3: Core ID 3, Socket ID 0
> >   # node0 meminfo  : total = 8085412 kB, free = 5316992 kB
> >   # node0 cpu list : 0-3
> > 
> > So, again, this was not introduced by this patchkit, but it is good that you did
> > these offline tests, so we can fix it!
> 
> Stephane, this was introduced in:
> 
>   commit fbe96f29ce4b33e0a22219cc7f5996d9157717e3
>   Author: Stephane Eranian <eranian@xxxxxxxxxx>
>   Date:   Fri Sep 30 15:40:40 2011 +0200
> 
>     perf tools: Make perf.data more self-descriptive (v8)
> 
> ------------------
> 
> When you write this part:
> 
>       - HEADER_NRCPUS: number of online/avail cpus
> 
> You do:
> 
> static int write_nrcpus(int fd, struct perf_header *h __used,
>                        struct perf_evlist *evlist __used)
> {
>        long nr;
>        u32 nrc, nra;
>        int ret;
> 
>        nr = sysconf(_SC_NPROCESSORS_CONF);
>        if (nr < 0)
>                return -1;
> 
>        nrc = (u32)(nr & UINT_MAX);
> 
>        nr = sysconf(_SC_NPROCESSORS_ONLN);
>        if (nr < 0)
>                return -1;
> 
>        nra = (u32)(nr & UINT_MAX);
> 
>        ret = do_write(fd, &nrc, sizeof(nrc));
>        if (ret < 0)
>                return ret;
> 
>        return do_write(fd, &nra, sizeof(nra));
> }
> 
> I.e. write what you called 'nrc' using what is in SC_NRPROCESSORS_CONF, that in
> the documentation for glibc reads:
> 
> ---------------------
> 
> http://www.gnu.org/software/libc/manual/html_node/Processor-Resources.html
> 
>   sysconf (_SC_NPROCESSORS_CONF)
> 
> which returns the number of processors the operating system configured. But it
> might be possible for the operating system to disable individual processors and
> so the call 
> 
> ---------------------
> 
> Which menas "NR_AVAILABLE", right?
> 
> But then you call a variable 'nra' which sounds like you think that what is in
> _SC_NPROCESSORS_ONLN is the "available" number of CPUs, which is confused a bit
> more by the glibc docs when refering to _SC_NPROCESSORS_ONLN:
> 
> ---------------------
>   sysconf (_SC_NPROCESSORS_ONLN)
> 
> returns the number of processors which are currently online (i.e., available). 
> ---------------------
> 
> Then, when printing the number of CPUs encoded in the perf.data file by the
> above write_nrcpus() routine, you did:
> 
> static void print_nrcpus(struct perf_header *ph, int fd, FILE *fp)
> {
>        ssize_t ret;
>        u32 nr;
> 
>        ret = read(fd, &nr, sizeof(nr));
>        if (ret != (ssize_t)sizeof(nr))
>                nr = -1; /* interpreted as error */
> 
>        if (ph->needs_swap)
>                nr = bswap_32(nr);
> 
>        fprintf(fp, "# nrcpus online : %u\n", nr);
> 
>        ret = read(fd, &nr, sizeof(nr));
>        if (ret != (ssize_t)sizeof(nr))
>                nr = -1; /* interpreted as error */
> 
>        if (ph->needs_swap)
>                nr = bswap_32(nr);
> 
>        fprintf(fp, "# nrcpus avail : %u\n", nr);
> }
> 
> You inverted it, no?
> 
> So, could you please check if the below patch can have your Acked-by?
> Namhyung?

Looks good to me.

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> 
> Thanks,
> 
> - Arnaldo
> 
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index 41814547da15..fce6634aebe2 100644
> --- a/tools/perf/util/header.c
> +++ b/tools/perf/util/header.c
> @@ -1438,7 +1438,7 @@ static int process_nrcpus(struct perf_file_section *section __maybe_unused,
>  	if (ph->needs_swap)
>  		nr = bswap_32(nr);
>  
> -	ph->env.nr_cpus_online = nr;
> +	ph->env.nr_cpus_avail = nr;
>  
>  	ret = readn(fd, &nr, sizeof(nr));
>  	if (ret != sizeof(nr))
> @@ -1447,7 +1447,7 @@ static int process_nrcpus(struct perf_file_section *section __maybe_unused,
>  	if (ph->needs_swap)
>  		nr = bswap_32(nr);
>  
> -	ph->env.nr_cpus_avail = nr;
> +	ph->env.nr_cpus_online = nr;
>  	return 0;
>  }
>  
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