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<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
<span style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px">Mathieu,</span></p>
<p><br>
<font color="#282828" face="Segoe UI WPC, Segoe UI, Tahoma, Microsoft Sans Serif, Verdana, sans-serif" size="2">I tried to send this email to lttng-dev@ but I didn't get any response. So I am sending this directly to you. I greatly appreciate your response.</font></p>
<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
<span style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px"><br>
</span></p>
<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
<span style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px">We are planning to use LTTng UST as it supports lot of interesting features, but have some performance concerns (as compared
with our in-house tracing tool). Please point me to the latest benchmark tests and performance results. <span style="color: rgb(40, 40, 40); font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);">On CPU Intel
Xeon E5-2680 v2 @ 2.80GHz, running Linux 3.6.11 and lttng 2.4.1, I am getting about 927 cycles (9270692144 cycles for 10000000 iterations). This seems to be lot higher than the documented results. In the paper </span><a href="https://lttng.org/files/papers/desnoyers.pdf" target="_blank" style="font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);">https://lttng.org/files/papers/desnoyers.pdf</a><span style="color: rgb(40, 40, 40); font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);"> the
average cost of tracepoint() with older ltt-usertrace-fast tracepoint is 297 cycles. Another link </span><a href="http://lttng.org/files/thesis/desnoyers-thesis-defense-2009-12-e1.pdf" target="_blank" style="font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);">http://lttng.org/files/thesis/desnoyers-thesis-defense-2009-12-e1.pdf</a><span style="color: rgb(40, 40, 40); font-family: 'Segoe UI WPC', 'Segoe UI', Tahoma, 'Microsoft Sans Serif', Verdana, sans-serif; font-size: 13px; background-color: rgb(255, 255, 255);"> says
cache hot tracepoint() cost is 238 cycles.</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);"></span></span></p>
<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
<br style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px; background-color:rgb(255,255,255)">
<span style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px; background-color:rgb(255,255,255)">I noticed that the tracepoint is making clock_gettime() and sched_getcpu() system calls.
With Linux kernel v3.6.11 and libc v2.13-38+deb7u3, I see that these system calls are not going through VDSO and hence costing more. I tried to add wrapper functions for these system calls to call __vdso_clock_gettime and __vdso_getcpu as upgrading libc was
not an option. With this change the cost of tracepoint() recording one integer dropped to 795 cycles (= 284 nsec on Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz). Still this number seems to be higher than earlier published numbers. </span></p>
<p style="color: rgb(0, 0, 0); font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 12pt;">
<br style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px; background-color:rgb(255,255,255)">
<span style="color:rgb(40,40,40); font-family:'Segoe UI WPC','Segoe UI',Tahoma,'Microsoft Sans Serif',Verdana,sans-serif; font-size:13px; background-color:rgb(255,255,255)">VBabu</span><br>
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