From: David Sharp <dhsharp@google.com>
To: Avi Kivity <avi@redhat.com>
Cc: rostedt@goodmis.org, linux-kernel@vger.kernel.org,
mrubin@google.com, kvm-devel <kvm@vger.kernel.org>
Subject: Re: [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall
Date: Tue, 7 Dec 2010 13:16:48 -0800 [thread overview]
Message-ID: <AANLkTinK7Zqh=GfFLeyJLxA4u2ozyVj-Ja435iBJPV13@mail.gmail.com> (raw)
In-Reply-To: <4CFDFCEF.3080708@redhat.com>
On Tue, Dec 7, 2010 at 1:22 AM, Avi Kivity <avi@redhat.com> wrote:
> On 12/06/2010 10:38 PM, David Sharp wrote:
>> On Sat, Dec 4, 2010 at 12:11 AM, Avi Kivity<avi@redhat.com> wrote:
>> > On 12/04/2010 02:13 AM, David Sharp wrote:
>> >>
>> >> Signed-off-by: David Sharp<dhsharp@google.com>
>> >> ---
>> >> arch/x86/kvm/trace.h | 8 ++++----
>> >> 1 files changed, 4 insertions(+), 4 deletions(-)
>> >>
>> >> diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
>> >> index a6544b8..ab41fb0 100644
>> >> --- a/arch/x86/kvm/trace.h
>> >> +++ b/arch/x86/kvm/trace.h
>> >> @@ -62,21 +62,21 @@ TRACE_EVENT(kvm_hv_hypercall,
>> >> TP_ARGS(code, fast, rep_cnt, rep_idx, ingpa, outgpa),
>> >>
>> >> TP_STRUCT__entry(
>> >> - __field( __u16, code )
>> >> - __field( bool, fast )
>> >> __field( __u16, rep_cnt )
>> >> __field( __u16, rep_idx )
>> >> __field( __u64, ingpa )
>> >> __field( __u64, outgpa )
>> >> + __field( __u16, code )
>> >> + __field( bool, fast )
>> >> ),
>> >>
>> >
>> > Looks like a pessimisation.
>> >
>> > Before: 24 bytes
>> > After: 32 bytes
>> >
>> > (on a 64-bit machine, assuming no packing)
>>
>> This patch is predicated on packing the event structures. And since
>> the ring buffer is 32-bit addressable, I don't attempt to improve
>> alignment beyond 32-bit boundaries.
>
> I don't understand this. Can you elaborate? What does "32-bit addressable"
> mean?
The ring buffer gives you space that is a multiple of 4 bytes in
length, and 32-bit aligned. Therefore it is useless to attempt to
align the structure beyond 32-bit boundaries, eg, a 64-bit boundary,
because it is unpredictable if the memory the structure will be
written to is at a 64-bit boundary (addr % 8 could be 0 or 4).
> And "predicated on packing the event structures"? Is the structure
> __attribute__((packed)), or is it not?
It is not packed in Linus' tree, but one of the patches before this
patch in this patch series adds __attribute__((packed)). This patch
assumes that the event packing patch has been applied. This patch
should not be applied if the packing patch is not (hence,
"predicated").
>
> --
> error compiling committee.c: too many arguments to function
>
>
next prev parent reply other threads:[~2010-12-07 21:17 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-12-04 0:13 [Patch 00/15] Reduce tracing payload size David Sharp
2010-12-04 0:13 ` [PATCH 01/15] tracing: Add a 'buffer_overwrite' debugfs file David Sharp
2010-12-04 1:57 ` Steven Rostedt
2010-12-08 20:15 ` David Sharp
2010-12-08 21:46 ` [PATCH] tracing: Add an 'overwrite' trace_option David Sharp
2010-12-14 0:39 ` David Sharp
2011-03-09 0:45 ` David Sharp
2011-03-11 9:45 ` [tip:perf/core] " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 02/15] ring_buffer.c: Remove unused #include <linux/trace_irq.h> David Sharp
2011-03-11 9:46 ` [tip:perf/core] ring-buffer: " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 03/15] ring_buffer: Align buffer_page struct allocations only to fit the flags David Sharp
2010-12-04 1:43 ` Steven Rostedt
2010-12-07 22:44 ` David Sharp
2010-12-04 0:13 ` [PATCH 04/15] ftrace: pack event structures David Sharp
2011-03-08 23:30 ` Steven Rostedt
2011-03-09 1:09 ` Steven Rostedt
2011-03-09 6:39 ` David Miller
2011-03-09 15:18 ` Steven Rostedt
2011-03-10 23:21 ` David Sharp
2011-03-11 3:37 ` Steven Rostedt
2011-03-09 13:01 ` Steven Rostedt
2010-12-04 0:13 ` [PATCH 05/15] ftrace: fix event alignment: ftrace:context_switch and ftrace:wakeup David Sharp
2011-03-11 9:48 ` [tip:perf/core] tracing: Fix " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 06/15] ftrace: fix event alignment: module:module_request David Sharp
2010-12-04 1:47 ` Steven Rostedt
2010-12-06 1:28 ` Li Zefan
2011-03-11 9:48 ` [tip:perf/core] tracing: Fix " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 07/15] ftrace: fix event alignment: kvm:kvm_hv_hypercall David Sharp
2010-12-04 1:49 ` Steven Rostedt
2010-12-04 8:11 ` Avi Kivity
2010-12-06 20:38 ` David Sharp
2010-12-07 9:22 ` Avi Kivity
2010-12-07 21:16 ` David Sharp [this message]
2010-12-08 9:18 ` Avi Kivity
2011-03-08 23:55 ` Steven Rostedt
2011-03-09 8:50 ` Avi Kivity
2011-03-09 12:54 ` Steven Rostedt
2011-03-09 13:01 ` Avi Kivity
2011-03-11 9:49 ` [tip:perf/core] tracing: Fix " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 08/15] ftrace: fix event alignment: mce:mce_record David Sharp
2010-12-04 1:50 ` Steven Rostedt
2010-12-09 13:33 ` Frederic Weisbecker
2011-03-11 9:49 ` [tip:perf/core] tracing: Fix " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 09/15] ftrace: fix event alignment: skb:kfree_skb David Sharp
2010-12-04 1:52 ` Steven Rostedt
2010-12-04 13:38 ` Neil Horman
2011-03-11 9:50 ` [tip:perf/core] tracing: Fix " tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 10/15] ftrace: fix event alignment: jbd2:* David Sharp
2010-12-04 1:52 ` Steven Rostedt
2011-03-09 0:03 ` Steven Rostedt
2011-03-09 0:31 ` Ted Ts'o
2011-03-09 0:41 ` Steven Rostedt
2010-12-04 0:13 ` [PATCH 11/15] ftrace: fix event alignment: ext4:* David Sharp
2010-12-04 1:53 ` Steven Rostedt
2011-03-09 0:04 ` Steven Rostedt
2010-12-04 0:13 ` [PATCH 12/15] trace_output.c: adjust conditional expression formatting David Sharp
2011-03-11 9:50 ` [tip:perf/core] tracing: Adjust conditional expression latency formatting tip-bot for David Sharp
2010-12-04 0:13 ` [PATCH 13/15] small_traces: Add config option to shrink trace events David Sharp
2010-12-04 1:56 ` Steven Rostedt
2010-12-04 2:33 ` David Sharp
2010-12-04 2:54 ` Steven Rostedt
2010-12-09 14:55 ` Frederic Weisbecker
2010-12-09 15:08 ` Steven Rostedt
2010-12-09 15:28 ` Frederic Weisbecker
2010-12-09 16:16 ` Mathieu Desnoyers
2011-03-09 0:23 ` Steven Rostedt
2010-12-04 0:13 ` [PATCH 14/15] small_traces: Remove trace output of large fields David Sharp
2010-12-04 0:13 ` [PATCH 15/15] small_traces: Remove 8 bytes from trace_entry David Sharp
2010-12-06 13:22 ` [Patch 00/15] Reduce tracing payload size Andi Kleen
2010-12-06 13:56 ` Ted Ts'o
2010-12-06 14:58 ` Andi Kleen
2010-12-06 16:17 ` Steven Rostedt
2010-12-06 16:31 ` Miguel Ojeda
2010-12-06 16:41 ` Andi Kleen
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