From: Qais Yousef <qais.yousef@arm.com>
To: peterz@infradead.org
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
vincent.donnefort@arm.com, mingo@redhat.com,
vincent.guittot@linaro.org, linux-kernel@vger.kernel.org,
valentin.schneider@arm.com, Phil Auld <pauld@redhat.com>
Subject: Re: [PATCH v2] sched/debug: Add new tracepoint to track cpu_capacity
Date: Mon, 7 Sep 2020 15:51:55 +0100 [thread overview]
Message-ID: <20200907145155.fsmeygi4fiypikzk@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20200907111320.GP2674@hirez.programming.kicks-ass.net>
On 09/07/20 13:13, peterz@infradead.org wrote:
> On Mon, Sep 07, 2020 at 11:48:45AM +0100, Qais Yousef wrote:
> > IMHO the above is a hack. Out-of-tree modules should rely on public headers and
> > exported functions only. What you propose means that people who want to use
> > these tracepoints in meaningful way must have a prebuilt kernel handy. Which is
> > maybe true for us who work in the embedded world. But users who run normal
> > distro kernels (desktop/servers) will fail to build against
>
> But this isn't really aimed at regular users. We're aiming this at
> developers (IIUC) so I dont really see this as a problem.
>
> > FWIW, I did raise this concern with Peter in 2019 OSPM and he was okay with the
> > exports as it's still not a contract and they can disappear anytime we want.
> > Migrating to using BTF is the right way forward IMO. I don't think what we have
> > here is out-of-control yet. Though I agree they're annoying.
>
> Right, we're hiding behind the explicit lack of ABI for modules.
>
> Anyway, CTF/BTF/random other crap that isn't DWARFs should work fine to
> replace all this muck. Just no idea what the state of any of that is.
So I was thinking of having a function that allows a module to read member of
struct rq (or any struct for that matters), but I think that's the harder
(though neater) way around.
Just compiled a kernel with CONFIG_DEBUG_INFO_BTF_INFO; and doing
$ pahole rq
struct rq {
raw_spinlock_t lock; /* 0 4 */
unsigned int nr_running; /* 4 4 */
long unsigned int last_blocked_load_update_tick; /* 8 8 */
unsigned int has_blocked_load; /* 16 4 */
/* XXX 12 bytes hole, try to pack */
call_single_data_t nohz_csd; /* 32 32 */
/* --- cacheline 1 boundary (64 bytes) --- */
unsigned int nohz_tick_stopped; /* 64 4 */
atomic_t nohz_flags; /* 68 4 */
unsigned int ttwu_pending; /* 72 4 */
/* XXX 4 bytes hole, try to pack */
u64 nr_switches; /* 80 8 */
.
.
.
}
dumps the struct rq {...}; which means one can easily use that to autogenerate
a header containing the structs they care about accessing for their running
kernel.
pahole automatically knows how to find /sys/kernel/btf/vmlinux to parse the
debug info btw.
The only caveat is that one has to recompile the module for each running
kernel; but that's acceptable I think. Not sure how many allow loading a module
that's not compiled for that particular kernel version anyway.
Note to try this you'll need pahole v1.16 or newer. And compiling pahole on
Ubuntu is a pain. I had to create a fedora docker image to compile it in.
So I think we have this already solved. Though not sure how to document it..
Thanks
--
Qais Yousef
next prev parent reply other threads:[~2020-09-07 14:57 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-28 9:00 [PATCH v2] sched/debug: Add new tracepoint to track cpu_capacity vincent.donnefort
2020-08-28 10:27 ` Qais Yousef
2020-08-28 17:10 ` Dietmar Eggemann
2020-08-28 17:26 ` Qais Yousef
2020-09-02 10:44 ` Dietmar Eggemann
2020-09-02 13:54 ` Phil Auld
2020-09-07 11:02 ` Qais Yousef
2020-09-08 13:19 ` Phil Auld
2020-09-08 15:22 ` Qais Yousef
2021-01-04 18:26 ` Qais Yousef
2021-01-04 18:59 ` Alexei Starovoitov
2021-01-05 11:38 ` Qais Yousef
2021-01-05 16:44 ` Alexei Starovoitov
2021-01-06 11:27 ` Qais Yousef
2021-01-06 23:42 ` Andrii Nakryiko
2021-01-07 11:23 ` Qais Yousef
2021-01-11 14:04 ` Peter Zijlstra
2021-01-11 14:08 ` Qais Yousef
2020-09-07 10:48 ` Qais Yousef
2020-09-07 11:13 ` peterz
2020-09-07 14:51 ` Qais Yousef [this message]
2020-09-08 11:17 ` Dietmar Eggemann
2020-09-08 15:17 ` Qais Yousef
2020-09-08 16:17 ` Dietmar Eggemann
2021-01-04 15:18 ` Qais Yousef
2020-10-05 7:43 ` [tip: sched/core] " tip-bot2 for Vincent Donnefort
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