Adding a new VFS Lttng module for performance testing

Ralph Böhme slow at
Mon Dec 17 16:50:52 UTC 2018


sorry, looks like we dropped the ball on this one.

On Wed, Oct 24, 2018 at 12:04:03PM +0800, deanraccoon wrote:
>I think syscalls only works for local file system. When I was tuning the samba 
>ceph/glusterfs module. Neither systemtap nor bpf could help me.

ah, I see. Well, you can trace arbitray functions with Systemtap, but after some 
more research I see another argument for having the ltt-ng VFS module. With 
Systemtap every enabled tracepoint that is excersized triggers a context switch 
as all metrics are gathered in the kernel by Systemtap. As a result for large 
number of enabled trace points (think: all syscalls) the performance impact on 
the process becomes significant.

With ltt-ng by contrast the metrics are collected in userspace so the costly 
context switch is avoided.

Can you send us an updated patchset on top of current master? We'll also need a 
manpage. I'll happily review and will help getting this integrated.


Ralph Boehme, Samba Team      
Samba Developer, SerNet GmbH
GPG-Fingerprint   FAE2C6088A24252051C559E4AA1E9B7126399E46

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