All of lore.kernel.org
 help / color / mirror / Atom feed
From: Alexei Starovoitov <ast@plumgrid.com>
To: "Wangnan (F)" <wangnan0@huawei.com>,
	Kaixu Xia <xiakaixu@huawei.com>,
	davem@davemloft.net, acme@kernel.org, mingo@redhat.com,
	a.p.zijlstra@chello.nl, masami.hiramatsu.pt@hitachi.com,
	jolsa@kernel.org, daniel@iogearbox.net
Cc: linux-kernel@vger.kernel.org, pi3orama@163.com,
	hekuang@huawei.com, netdev@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers
Date: Mon, 12 Oct 2015 21:16:59 -0700	[thread overview]
Message-ID: <561C85BB.3000505@plumgrid.com> (raw)
In-Reply-To: <561C7FBE.4000104@huawei.com>

On 10/12/15 8:51 PM, Wangnan (F) wrote:
>> why 'set disable' is needed ?
>> the example given in cover letter shows the use case where you want
>> to receive samples only within sys_write() syscall.
>> The example makes sense, but sys_write() is running on this cpu, so just
>> disabling it on the current one is enough.
>>
>
> Our real use case is control of the system-wide sampling. For example,
> we need sampling all CPUs when smartphone start refershing its display.
> We need all CPUs because in Android system there are plenty of threads
> get involed into this behavior. We can't achieve this by controling
> sampling on only one CPU. This is the reason we need 'set enable'
> and 'set disable'.

ok, but that use case may have different enable/disable pattern.
In sys_write example ultra-fast enable/disable is must have, since
the whole syscall is fast and overhead should be minimal.
but for display refresh? we're talking milliseconds, no?
Can you just ioctl() it from user space?
If cost of enable/disable is high or the time range between toggling is
long, then doing it from the bpf program doesn't make sense. Instead
the program can do bpf_perf_event_output() to send a notification to
user space that condition is met and the user space can ioctl() events.


  reply	other threads:[~2015-10-13  4:17 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-10-12  9:02 [RFC PATCH 0/2] bpf: enable/disable events stored in PERF_EVENT_ARRAY maps trace data output when perf sampling Kaixu Xia
2015-10-12  9:02 ` [RFC PATCH 1/2] perf: Add the flag sample_disable not to output data on samples Kaixu Xia
2015-10-12 12:02   ` Peter Zijlstra
2015-10-12 12:05     ` Wangnan (F)
2015-10-12 12:12       ` Peter Zijlstra
2015-10-12 14:14   ` kbuild test robot
2015-10-12 19:20   ` Alexei Starovoitov
2015-10-13  2:30     ` xiakaixu
2015-10-13  3:10       ` Alexei Starovoitov
2015-10-13 12:00   ` Sergei Shtylyov
2015-10-12  9:02 ` [RFC PATCH 2/2] bpf: Implement bpf_perf_event_sample_enable/disable() helpers Kaixu Xia
2015-10-12 19:29   ` Alexei Starovoitov
2015-10-13  3:27     ` Wangnan (F)
2015-10-13  3:39       ` Alexei Starovoitov
2015-10-13  3:51         ` Wangnan (F)
2015-10-13  4:16           ` Alexei Starovoitov [this message]
2015-10-13  4:34             ` Wangnan (F)
2015-10-13  5:15               ` Alexei Starovoitov
2015-10-13  6:57                 ` Wangnan (F)
2015-10-13 10:54                 ` He Kuang
2015-10-13 11:07                   ` Wangnan (F)
2015-10-14  5:14                   ` Alexei Starovoitov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=561C85BB.3000505@plumgrid.com \
    --to=ast@plumgrid.com \
    --cc=a.p.zijlstra@chello.nl \
    --cc=acme@kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=hekuang@huawei.com \
    --cc=jolsa@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=masami.hiramatsu.pt@hitachi.com \
    --cc=mingo@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=pi3orama@163.com \
    --cc=wangnan0@huawei.com \
    --cc=xiakaixu@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.