<div dir="ltr"><div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Jan 21, 2020 at 11:55 AM Gionatan Danti <<a href="mailto:g.danti@assyoma.it">g.danti@assyoma.it</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Il 20-01-2020 16:30 Gionatan Danti ha scritto:<br>
> So, I have some questions:<br>
> - why performance are so low with fsync?<br>
> - why do I have so low IOPs (20/30) for minutes?<br>
> - what is capping the non-fsync test?<br>
> - why both glusterd and glusterfd are so CPU intensive? I can<br>
> understand glusterfd itself requiring more CPU, but glusterd should<br>
> only manage the other processes and send the volume information to<br>
> asking client, right?<br>
<br>
An update: the very low IOPs were caused by TCP retransmission on one of <br>
the two boxes. After that problem was fixed, no such low performance was <br>
recorded.<br></blockquote><div><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">How did you fix this?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">How did you spot this?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
I also think that the non-fsync tests, with about 5000 IOPs, are cappaed <br>
by the 1000BaseT round trip time.<br>
<br>
Some questions remain:<br>
- why performance are so low with fsync? (about 250 IOPs)<br></blockquote><div><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">fsync requires each write to land on disk and get an ack on it - it's probably the slowest kind of write you can imagine, and you seem be doing it for every small (4K?) block.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">This is not very realistic. But in your case you say you are writing to /dev/shm, so that is strange. Can you try with a different fio engine and see what you get?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">What are you trying to test here?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
- why both glusterd and glusterfd are so CPU intensive?<br></blockquote><div><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Good question. Perhaps profiling would help here. Perhaps too many threads are contending for CPU? Some lock contention?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Y.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<br>
Thanks.<br>
<br>
-- <br>
Danti Gionatan<br>
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