From: Arjan van de Ven <arjan@linux.intel.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 13/13 -next] tracing: Remove the extra 4 bytes of padding in events
Date: Mon, 21 Jan 2013 15:13:16 -0800 [thread overview]
Message-ID: <50FDCB8C.40208@linux.intel.com> (raw)
In-Reply-To: <20130121211729.357828882@goodmis.org>
On 1/21/2013 1:14 PM, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> Due to a userspace issue with PowerTop v1, which hardcoded
> the offset of event fields that it was using, it broke when
> we removed the Big Kernel Lock counter from the event header.
>
> (commit e6e1e2593 "tracing: Remove lock_depth from event entry")
>
> Because this broke userspace, it was determined that we must
> keep those 4 bytes around.
>
> (commit a3a4a5acd "Regression: partial revert "tracing: Remove lock_depth from event entry"")
>
> This unfortunately wastes space in the ring buffer. 4 bytes per
> event, where a lot of events are just 24 bytes. That's 16% of the
> buffer wasted. A million events will add 4 megs of white space
> into the buffer.
>
> It was later noticed that PowerTop v1 could not work on systems
> where the kernel was 64 bit but the userspace was 32 bits.
> The reason was because the offsets are different between the
> two and the hard coded offset of one would not work with the other.
>
> With PowerTop v2, it implemented the same interface that both
> perf and trace-cmd use. That is, it reads the format file of
> the event to find the offsets of the fields it needs. This fixes
> the problem with running powertop on a 32 bit userspace running
> on a 64 bit kernel. It also no longer requires the 4 byte padding.
>
> As PowerTop v2 has been out for a while, and is included in all
> major distributions, it is time that we can safely remove the
> 4 bytes of padding. Users of PowerTop v1 should upgrade to
> PowerTop v2.
>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
this only impacts the users of the 2.0beta series (which, while arguably staying around for too long, is now very very obsolete and
replaced by the final in all distros that I'm aware of)
Acked-By: Arjan van de Ven <arjan@linux.intel.com>
prev parent reply other threads:[~2013-01-21 23:13 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-21 21:14 [PATCH 00/13 -next] [For linux-next] tracing: Review of changes Steven Rostedt
2013-01-21 21:14 ` [PATCH 01/13 -next] tracing: Fix sparse warning with is_signed_type() macro Steven Rostedt
2013-01-21 21:14 ` [PATCH 02/13 -next] ring-buffer: Remove unnecessary recusive call in rb_advance_iter() Steven Rostedt
2013-01-21 21:14 ` [PATCH 03/13 -next] tracing: Use this_cpu_ptr per-cpu helper Steven Rostedt
2013-01-21 21:14 ` [PATCH 04/13 -next] tracing: Verify target file before registering a uprobe event Steven Rostedt
2013-01-21 21:14 ` [PATCH 05/13 -next] tracing/syscalls: Make local functions static Steven Rostedt
2013-01-21 21:14 ` [PATCH 06/13 -next] tracing: Add checks if tr->buffer is NULL in tracing_reset{_online_cpus} Steven Rostedt
2013-01-21 21:14 ` [PATCH 07/13 -next] tracing: Remove unneeded check of max_tr->buffer before tracing_reset Steven Rostedt
2013-01-21 21:14 ` [PATCH 08/13 -next] tracing/lockdep: Disable lockdep first in entering NMI Steven Rostedt
2013-01-21 21:14 ` [PATCH 09/13 -next] tracing/fgraph: Add max_graph_depth to limit function_graph depth Steven Rostedt
2013-01-21 21:14 ` [PATCH 10/13 -next] ftrace: Move ARCH_SUPPORTS_FTRACE_SAVE_REGS in Kconfig Steven Rostedt
2013-01-21 21:14 ` [PATCH 11/13 -next] kprobes/x86: Move ftrace-based kprobe code into kprobes-ftrace.c Steven Rostedt
2013-01-21 21:14 ` [PATCH 12/13 -next] kprobes/x86: Move kprobes stuff under arch/x86/kernel/kprobes/ Steven Rostedt
2013-01-21 21:14 ` [PATCH 13/13 -next] tracing: Remove the extra 4 bytes of padding in events Steven Rostedt
2013-01-21 23:13 ` Arjan van de Ven [this message]
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