From: Jason Baron <jbaron@redhat.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Ian Munsie <imunsie@au1.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@ozlabs.org,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Michael Ellerman <michael@ellerman.id.au>,
Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
Masami Hiramatsu <mhiramat@redhat.com>
Subject: Re: [PATCH 08/40] tracing: remove syscall bitmaps in preparation for compat support
Date: Wed, 23 Jun 2010 15:34:56 -0400 [thread overview]
Message-ID: <20100623193455.GE2680@redhat.com> (raw)
In-Reply-To: <20100623191454.GC2680@redhat.com>
On Wed, Jun 23, 2010 at 03:14:54PM -0400, Jason Baron wrote:
> On Wed, Jun 23, 2010 at 11:16:44AM -0400, Steven Rostedt wrote:
> > On Wed, 2010-06-23 at 20:02 +1000, Ian Munsie wrote:
> > > From: Jason Baron <jbaron@redhat.com>
> > >
> > > In preparation for compat syscall tracing support, let's store the enabled
> > > syscalls, with the struct syscall_metadata itself. That way we don't duplicate
> > > enabled information when the compat table points to an entry in the regular
> > > syscall table. Also, allows us to remove the bitmap data structures completely.
> > >
> > > Signed-off-by: Jason Baron <jbaron@redhat.com>
> > > Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
> > > ---
> > > include/linux/syscalls.h | 8 +++++++
> > > include/trace/syscall.h | 4 +++
> > > kernel/trace/trace_syscalls.c | 42 +++++++++++++++++++---------------------
> > > 3 files changed, 32 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> > > index 86f082b..755d05b 100644
> > > --- a/include/linux/syscalls.h
> > > +++ b/include/linux/syscalls.h
> > > @@ -163,6 +163,10 @@ extern struct trace_event_functions exit_syscall_print_funcs;
> > > .nb_args = nb, \
> > > .types = types_##sname, \
> > > .args = args_##sname, \
> > > + .ftrace_enter = 0, \
> > > + .ftrace_exit = 0, \
> > > + .perf_enter = 0, \
> > > + .perf_exit = 0, \
> >
> > I really hate this change!
> >
> > You just removed a nice compressed bitmap (1 bit per syscall) to add 4
> > bytes per syscall. On my box I have 308 syscalls being traced. That was
> > 308 bits per bitmask = 39 bytes * 2 = 78 * 2 (perf and ftrace) = 156.
> >
> > Now we have 8 bytes per syscall (enter and exit), which is 1232 bytes.
> >
> > Thus this change added 1076 bytes.
> >
> > This may not seem as much, but the change is not worth 1K. Can't we just
> > add another bitmask or something for the compat case?
> >
> > I also hate the moving of ftrace and perf internal data to an external
> > interface.
> >
> > -- Steve
> >
>
> I made this change (I also wrote the original bitmap), b/c compat
> syscalls can share "regular" syscalls. That is the compat syscall table
> points to syscalls from non-compat mode. (looking at ia32 on x86 it
> looks like at least half).
>
> Thus, if we continue along the bitmap path, we would have to introduce
> another 4 bitmaps for compat. 2 for enter and exit and 2 for perf and
> ftrace. Thus, using your math above: 39 bytes * 8 = 312 bytes. So
> approximately 1 byte per system call.
>
> Instead, if we store this data in the syscall metadata, we actually only
> need 4 bits per syscall. Now, the above implementation uses 4 chars,
> where we really only need 1 char (or really 4 bits, which we could
> eventually store in the last last bit of the four existing pointer
> assuming they are 2 byte aligned for no increased storage space at all).
> But even assuming we use 1 byte per system call we are going to have in
> the worse case the above 312 bytes + (1 byte * # of non-shared compat
> syscalls). So, yes we might need a little more storage in this scheme.
> Another consideration too, is obviously the alignment of
> syscall_metadata, since the extra 1 byte, might be more...
>
> However, we don't have to compute the location of the bits in the
> compat syscall map each time a tracing syscall is enable/disable. This
> would be more expensive, especially if we don't store the compat syscall
> number with each syscall meta data structure (which you have proposed
> dropping). So with compat syscalls, we are setting two bit locations
> with each enable/disable instead of 1 with this new scheme.
>
> Also, I think the more important reason to store these bits in the
> syscall meta data structure is simplicity. Not all arches start their tables
> counting from 0 (requiring a constant shift factor), and obviously we
> waste bits for non-implemented syscalls. I don't want to have to deal
> with these arch specific implementation issues, if I don't need to.
>
> thanks,
>
> -Jason
>
Actually, looking at this further, what we probably want to do change
the "int nb_args" field, which is already in syscall_metadata into a bit
field. nb_args I think can be at most 6, or 3 bits, and we only need 4
bits for storing the enabled/disabled data, so we could even make it a
char. Thus, actually saving space with this patch :) (at least as far as
the syscall_metadata field is concerned).
thanks,
-Jason
next prev parent reply other threads:[~2010-06-23 19:35 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-23 10:02 ftrace syscalls, PowerPC: Various fixes, Compat Syscall support and PowerPC implementation, V2 Ian Munsie
2010-06-23 10:02 ` [PATCH 01/40] ftrace syscalls: don't add events for unmapped syscalls Ian Munsie
2010-06-23 15:02 ` Steven Rostedt
2010-06-29 1:18 ` Ian Munsie
2010-06-23 10:02 ` [PATCH 02/40] ftrace syscalls: Make arch_syscall_addr weak Ian Munsie
2010-06-23 10:02 ` [PATCH 03/40] ftrace syscalls: Allow arch specific syscall symbol matching Ian Munsie
2010-06-23 10:02 ` [PATCH 04/40] trace, powerpc: Implement raw syscall tracepoints on PowerPC Ian Munsie
2010-06-23 10:02 ` [PATCH 05/40] x86: add NR_syscalls_compat, make ia32 syscall table visible Ian Munsie
2010-06-23 10:02 ` [PATCH 06/40] x86: add arch_compat_syscall_addr() Ian Munsie
2010-06-23 10:02 ` [PATCH 08/40] tracing: remove syscall bitmaps in preparation for compat support Ian Munsie
2010-06-23 15:16 ` Steven Rostedt
2010-06-23 19:14 ` Jason Baron
2010-06-23 19:34 ` Jason Baron [this message]
2010-06-23 19:45 ` Steven Rostedt
2010-06-23 10:02 ` [PATCH 09/40] tracing: move __start_ftrace_events and __stop_ftrace_events to header file Ian Munsie
2010-06-23 10:02 ` [PATCH 10/40] tracing: add tracing support for compat syscalls Ian Munsie
2010-06-23 15:26 ` Steven Rostedt
2010-06-23 16:02 ` Frederic Weisbecker
2010-06-23 10:02 ` [PATCH 11/40] syscalls: add ARCH_COMPAT_SYSCALL_DEFINE() Ian Munsie
2010-06-23 10:02 ` [PATCH 12/40] x86, compat: convert ia32 layer to use Ian Munsie
2010-06-23 10:14 ` Christoph Hellwig
2010-06-23 10:36 ` Frederic Weisbecker
2010-06-23 10:46 ` Christoph Hellwig
2010-06-23 11:41 ` Frederic Weisbecker
2010-06-23 19:23 ` H. Peter Anvin
2010-06-24 14:37 ` Christoph Hellwig
2010-06-23 10:02 ` [PATCH 13/40] syscalls: add new COMPAT_SYSCALL_DEFINE#N() macro Ian Munsie
2010-06-23 10:02 ` [PATCH 14/40] compat: convert to use COMPAT_SYSCALL_DEFINE#N() Ian Munsie
2010-06-23 10:02 ` [PATCH 15/40] compat: convert fs compat to use COMPAT_SYSCALL_DEFINE#N() macros Ian Munsie
2010-06-23 10:02 ` [PATCH 16/40] tags: recognize compat syscalls Ian Munsie
2010-06-24 12:02 ` Michal Marek
2010-06-23 10:02 ` [PATCH 17/40] tracing: make a "compat_syscalls" tracing subsys Ian Munsie
2010-06-23 10:02 ` [PATCH 18/40] compat_syscalls: introduce CONFIG_COMPAT_FTRACE_SYSCALLS Ian Munsie
2010-06-23 10:03 ` [PATCH 19/40] trace syscalls: Remove redundant syscall_nr checks Ian Munsie
2010-06-23 10:03 ` [PATCH 20/40] trace syscalls: Considder compat_syscall_nr when verifying syscall_nr Ian Munsie
2010-06-23 10:03 ` [PATCH 21/40] trace syscalls, PPC: Add ftrace compat syscall support for PPC64 Ian Munsie
2010-06-23 10:03 ` [PATCH 22/40] trace syscalls, PPC: Convert syscalls to SYSCALL_DEFINE Ian Munsie
2010-06-23 10:03 ` [PATCH 23/40] trace syscalls, PPC: Convert ppc32 compat syscalls to COMPAT_SYSCALL Ian Munsie
2010-06-23 10:03 ` [PATCH 24/40] trace syscalls, PPC: Convert more " Ian Munsie
2010-06-23 10:03 ` [PATCH 25/40] trace syscalls: Refactor syscall metadata creation Ian Munsie
2010-06-23 10:03 ` [PATCH 26/40] trace syscalls, PPC: Add PPC_REGS_SYSCALL_DEFINE macros Ian Munsie
2010-06-23 10:03 ` [PATCH 27/40] trace syscalls: Add COMPAT_SYSCALL_DEFINE0 macro Ian Munsie
2010-06-23 10:03 ` [PATCH 28/40] trace syscalls, PPC: Convert syscalls using regs to REGS_SYSCALL_DEFINE macros Ian Munsie
2010-06-23 10:03 ` [PATCH 29/40] trace syscalls, PPC: Convert ppc32_ syscalls to ARCH_COMPAT_SYSCALL_DEFINE Ian Munsie
2010-06-23 10:03 ` [PATCH 30/40] trace syscalls: Convert remaining kernel/compat.c syscalls to COMPAT_SYSCALL_DEFINE Ian Munsie
2010-06-23 10:03 ` [PATCH 33/40] trace syscalls: Infrastructure for syscalls different return types Ian Munsie
2010-06-23 10:03 ` [PATCH 34/40] trace syscalls: Convert generic syscalls without long return type Ian Munsie
2010-06-23 10:03 ` [PATCH 35/40] trace syscalls, PPC: Convert PPC syscalls without long return types Ian Munsie
2010-06-23 10:03 ` [PATCH 36/40] trace syscalls: Early terminate search for sys_ni_syscall Ian Munsie
2010-06-23 10:03 ` [PATCH 37/40] trace syscalls: Print out unmapped syscalls at boot Ian Munsie
2010-06-23 10:03 ` [PATCH 38/40] trace syscalls: Remove redundant test for unmapped compat syscalls Ian Munsie
2010-06-23 10:03 ` [PATCH 39/40] trace syscalls: Clean confusing {s,r,}name and fix ABI breakage Ian Munsie
2010-06-23 18:03 ` Jason Baron
2010-06-29 1:02 ` Ian Munsie
2010-06-23 10:03 ` [PATCH 40/40] trace syscalls, PPC: Convert morphing native/compat syscalls Ian Munsie
[not found] ` <1277287401-28571-32-git-send-email-imunsie@au1.ibm.com>
[not found] ` <4C21DFBA.2070202@linux.intel.com>
[not found] ` <20100623102931.GB5242@nowhere>
[not found] ` <4C21E3F8.9000405@linux.intel.com>
2010-06-24 12:05 ` [PATCH 31/40] trace syscalls: Convert various generic compat syscalls Michal Marek
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