Re: [RFC PATCH 3/3] kernel tracing prototype

From: Jiaying Zhang
Date: Fri Dec 05 2008 - 13:36:49 EST

On Fri, Dec 5, 2008 at 7:34 AM, Frank Ch. Eigler <fche@xxxxxxxxxx> wrote:
> Jiaying Zhang <jiayingz@xxxxxxxxxx> writes:
>> To better answer the question why we want to implement a new kernel
>> tracing prototype, here are some performance results we collected before
>> with the tbench benchmark.
> Thanks.
>> - vanilla 2.6.26 kernel, CONFIG_MARKERS=n
>> Throughput 759.352 MB/sec 4
>> - markers compiled in, tracing disabled
>> Throughput 754.18 MB/sec 4
> Is your kernel built with -freorder-blocks? This option dramatically
> reduces the cost of inactive markers/tracepoints.
No. I will try this this flag and let you know if I see any
performance difference.
Thanks for your suggestion!

>> - tracing syscall entry/exit, use markers, not logging data to ring_buffer
>> Throughput 715.68 MB/sec 4
>> - tracing syscall entry/exit, use markers, logging data to ring_buffer
>> Throughput 654.056 MB/sec 4
> (By the way, how are you doing syscall entry/exit tracing?)
The way we trace syscall entry/exit is similar to the approach
used in LTTng. When tracing is enabled, a special flag,
TIF_KERNEL_TRACE is set so syscall entry and exit call special
syscall_trace_enter and syscall_trace_exit that are patched
to call trace_mark in our old prototype.


> - FChE
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