Lustre discuss - Jun 2013 - RPCs in flight

Hi Patrick,

This setting reflects how much network IO, in the form of unacknowledged RPCs, a
client can have sent (in flight) at any one time.

A setting of 8 would mean that the client can have 8 RPC''s out to each
OST.

It affects performance in that a client, which might otherwise be waiting for
RPC replies, can keep sending and not block - helpful for large asynchronous IO.

Of course, if too many clients are sending too much and overwhelm the storage
servers, then performance could be negatively impacted as well.

--
Brett Lee
Sr. Systems Engineer
Intel High Performance Data Division

From: lustre-discuss-bounces-aLEFhgZF4x6X6Mz3xDxJMA@public.gmane.org
[mailto:lustre-discuss-bounces@lists.lustre.org] On Behalf Of Chan Ching Yu,
Patrick
Sent: Thursday, June 27, 2013 4:57 PM
To: lustre-discuss-aLEFhgZF4x6X6Mz3xDxJMA@public.gmane.org
Subject: [Lustre-discuss] RPCs in flight

Dear all,

Just raise a probably stupid question. I always see the word "RPCs in
flight".

What does it mean? How does it affect the performance?

Thanks very much.




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> [ ... ] “RPCs in flight”. What does it mean? How does it
> affect the performance?
It means "sent but not yet received", and the time during which
it is "in flight" is called latency/delay.

Latency in general, and in particular RPC latency in Lustre,
matters a great deal to some important aspects of "performance".
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