review/test: NFS patch to use pagesize mbuf clusters

[Marcelo Araujo]

Hello Rick,

I have couple machines with 10G interface capable with TSO.
Which kind of result do you expecting? Is it a speed up in read?

I'm gonna make some tests today, but against 9.1-RELEASE, where my servers
are working on.

Best Regards,



2014-03-18 9:26 GMT+08:00 Rick Macklem <rmacklem at uoguelph.ca>:

> Hi,
>
> Several of the TSO capable network interfaces have a limit of
> 32 mbufs in the transmit mbuf chain (the drivers call these transmit
> segments, which I admit I find confusing).
>
> For a 64K read/readdir reply or 64K write request, NFS passes
> a list of 34 mbufs down to TCP. TCP will split the list, since
> it is slightly more than 64K bytes, but that split will normally
> be a copy by reference of the last mbuf cluster. As such, normally
> the network interface will get a list of 34 mbufs.
>
> For TSO enabled interfaces that are limited to 32 mbufs in the
> list, the usual workaround in the driver is to copy { real copy,
> not copy by reference } the list to 32 mbuf clusters via m_defrag().
> (A few drivers use m_collapse() which is less likely to succeed.)
>
> As a workaround to this problem, the attached patch modifies NFS
> to use larger pagesize clusters, so that the 64K RPC message is
> in 18 mbufs (assuming a 4K pagesize).
>
> Testing on my slow hardware which does not have TSO capability
> shows it to be performance neutral, but I believe avoiding the
> overhead of copying via m_defrag() { and possible failures
> resulting in the message never being transmitted } makes this
> patch worth doing.
>
> As such, I'd like to request review and/or testing of this patch
> by anyone who can do so.
>
> Thanks in advance for your help, rick
> ps: If you don't get the attachment, just email and I'll
>     send you a copy.
>
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-- 
Marcelo Araujo
araujo at FreeBSD.org