linux-kernel - Re: [RFC PATCH v4 10/29] bpf tools: Collect map definitions from 'maps' section

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Message-ID: <20150528060957.GA21013@Alexeis-MBP.westell.com>
Date:	Wed, 27 May 2015 23:09:58 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	paulus@...ba.org, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	acme@...nel.org, namhyung@...nel.org, jolsa@...nel.org,
	dsahern@...il.com, daniel@...earbox.net, brendan.d.gregg@...il.com,
	masami.hiramatsu.pt@...achi.com, lizefan@...wei.com,
	linux-kernel@...r.kernel.org, pi3orama@....com,
	xiakaixu 00238161 <xiakaixu@...wei.com>
Subject: Re: [RFC PATCH v4 10/29] bpf tools: Collect map definitions from
 'maps' section

On Thu, May 28, 2015 at 11:09:50AM +0800, Wangnan (F) wrote:
> 
> However this breaks a law in current design that opening phase doesn't
> talk to kernel with sys_bpf() at all. All related staff is done in loading
> phase. This principle ensures that in every systems, no matter it support
> sys_bpf() or not, can read eBPF object without failure.

I see, so you want 'parse elf' and 'create maps + load programs'
to be separate phases?
Fair enough. Then please add a call to release the information
collected from elf after program loading is done.
relocations and other things are not needed at that point.

> Moreover, we are planning to introduce hardware PMU to eBPF in the way like
> maps,
> to give eBPF programs the ability to access hardware PMU counter. I haven't

that's very interesting. Please share more info when you can :)
If I understood it right, you want in-kernel bpf to do aggregation
and filtering of pmu counters ?
And computing a number of cache misses between two kprobe events?
I can see how I can use that to measure not only time
taken by syscall, but number of cache misses occurred due
to syscall. Sounds very useful!

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