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Date: Tue, 19 May 2015 16:27:02 -0600
From: David Ahern <dsahern@gmail.com>
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To: Namhyung Kim <namhyung@kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
CC: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Jiri Olsa <jolsa@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Andi Kleen <andi@firstfloor.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 38/40] perf session: Handle index files generally
References: <1431909055-21442-1-git-send-email-namhyung@kernel.org> <1431909055-21442-39-git-send-email-namhyung@kernel.org>
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On 5/17/15 6:30 PM, Namhyung Kim wrote:
> The current code assumes that the number of index item and cpu are
> matched so it creates that number of threads.  But it's not the case
> of non-system-wide session or data came from different machine.
>
> Just creates threads at most number of online cpus and process data.

-----8<-----

> @@ -1717,6 +1742,7 @@ int perf_session__process_events_mt(struct perf_session *session, void *arg)
>   	int err, i, k;
>   	int nr_index = session->header.nr_index;
>   	u64 size = perf_data_file__size(file);
> +	int nr_thread = sysconf(_SC_NPROCESSORS_ONLN);

It's not clear to me how this multi-threaded perf is going to work on 
large systems especially this patch if a system has holes in the active 
cpus. e.g,

# lscpu
Architecture:          sparc64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Big Endian
CPU(s):                704
On-line CPU(s) list: 
32-63,128-223,256-351,384-479,576-831,864-927,960-1023
Thread(s) per core:    12
Core(s) per socket:    18
Socket(s):             3
NUMA node(s):          4
NUMA node0 CPU(s):     32-63,128-223
NUMA node1 CPU(s):     256-351,384-479
NUMA node2 CPU(s):     576-767
NUMA node3 CPU(s):     768-831,864-927,960-1023

So you are going to spawn 704 threads? Each thread handles a per-cpu buffer?

yes, I still need to find time to take if for a test drive; maybe by the 
end of the week.

David