LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: linux-kernel@vger.kernel.org, Linus Torvalds <torvalds@osdl.org>,
	Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@redhat.com>,
	Greg Kroah-Hartman <gregkh@suse.de>,
	Christoph Hellwig <hch@infradead.org>,
	ltt-dev@shafik.org, systemtap@sources.redhat.com,
	Douglas Niehaus <niehaus@eecs.ku.edu>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 05/05] Linux Kernel Markers, non optimised architectures
Date: Fri, 12 Jan 2007 00:00:32 -0500	[thread overview]
Message-ID: <20070112050032.GA14100@Krystal> (raw)
In-Reply-To: <45A710F8.7000405@yahoo.com.au>

* Nick Piggin (nickpiggin@yahoo.com.au) wrote:
> Mathieu Desnoyers wrote:
> 
> >+#define MARK(name, format, args...) \
> >+	do { \
> >+		static marker_probe_func *__mark_call_##name = \
> >+					__mark_empty_function; \
> >+		volatile static char __marker_enable_##name = 0; \
> >+		static const struct __mark_marker_c __mark_c_##name \
> >+			__attribute__((section(".markers.c"))) = \
> >+			{ #name, &__mark_call_##name, format } ; \
> >+		static const struct __mark_marker __mark_##name \
> >+			__attribute__((section(".markers"))) = \
> >+			{ &__mark_c_##name, &__marker_enable_##name } ; \
> >+		asm volatile ( "" : : "i" (&__mark_##name)); \
> >+		__mark_check_format(format, ## args); \
> >+		if (unlikely(__marker_enable_##name)) { \
> >+			preempt_disable(); \
> >+			(*__mark_call_##name)(format, ## args); \
> >+			preempt_enable_no_resched(); \
> 
> Why not just preempt_enable() here?
> 

Because the preempt_enable() macro contains preempt_check_resched(), which
may call preempt_schedule() which leads us to a call to schedule(). Therefore,
all those very interesting scheduler functions would cause an infinite
recursive scheduler call if we marked schedule() and used preempt_enable() in
the marker.

The primary goal for the markers (and the probes that attaches to them) is to
have the fewest side-effects possible : any kernel method called from an
instrumentation site adds this precise kernel method to the "cannot be
instrumented" list, which I want to keep as small possible.

Mathieu

-- 
OpenPGP public key:              http://krystal.dyndns.org:8080/key/compudj.gpg
Key fingerprint:     8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68 

  reply	other threads:[~2007-01-12  5:00 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-12  0:02 [PATCH 00/05] Linux Kernel Markers Mathieu Desnoyers
2007-01-12  0:02 ` [PATCH 01/05] Linux Kernel Markers : Kconfig menus Mathieu Desnoyers
2007-01-12  0:02 ` [PATCH 02/05] Linux Kernel Markers, architecture independant code Mathieu Desnoyers
2007-01-12  0:02 ` [PATCH 03/05] Linux Kernel Markers : powerpc optimisation Mathieu Desnoyers
2007-01-12  0:02 ` [PATCH 04/05] Linux Kernel Markers : i386 optimisation Mathieu Desnoyers
2007-01-12  0:02 ` [PATCH 05/05] Linux Kernel Markers, non optimised architectures Mathieu Desnoyers
2007-01-12  4:39   ` Nick Piggin
2007-01-12  5:00     ` Mathieu Desnoyers [this message]
2007-01-12  5:09       ` Nick Piggin
2007-01-12 17:15         ` Mathieu Desnoyers
2007-01-12 17:43           ` Mathieu Desnoyers
2007-01-12 18:23         ` [PATCH 05/05] update - " Mathieu Desnoyers

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=20070112050032.GA14100@Krystal \
    --to=mathieu.desnoyers@polymtl.ca \
    --cc=akpm@osdl.org \
    --cc=gregkh@suse.de \
    --cc=hch@infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ltt-dev@shafik.org \
    --cc=mingo@redhat.com \
    --cc=nickpiggin@yahoo.com.au \
    --cc=niehaus@eecs.ku.edu \
    --cc=systemtap@sources.redhat.com \
    --cc=tglx@linutronix.de \
    --cc=torvalds@osdl.org \
    --subject='Re: [PATCH 05/05] Linux Kernel Markers, non optimised architectures' \
    /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

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).