On Jan 11, 2007, at 1:14 PM, Scott Atchley wrote:
On Jan 11, 2007, at 11:31 AM, Sam Lang wrote:
On Jan 10, 2007, at 1:05 PM, Scott Atchley wrote:
Hi all,
I used MPE to measure send, sendunexpected and recv on the client
during pvfs2-cp (from the client to the server) of a (just less
than) 256 MB file. This is using older 2.4 GHz Xeons with MX-2G
(2 Gb/s line rate). I am using FlowBufferSizeBytes of 1 MB. I am
using the default FlowBuffersPerFlow. The server did not generate
a log and I am looking into why.
Hi Scott,
Ignore yesterday's email, I was thinking that the events included
both the client and server, but you're only using MPE on the client.
No problem. I still do not know why I cannot get a log from the
server.
This first image shows the entire copy of the file from client to
server. Recv are blue, send are red and sendunexpected are
orange. There 25 transfer of 10 MB each and the 26th transfer is
~5.5 MB. Note that there are distinct gaps between transfers in
the range of 17-18 msecs.
<pvfs2-cp-3.png>
As I said, I was confused yesterday. These gaps are entirely on
the client. The end of one blue column marks the receive of the
write ack completing, and the start of the next column marks the
beginning of the next request. The only thing that pvfs2-cp is
doing in the meantime, is reading the next 10MB of the local
file. I guess you're getting about 55 MB/s from that local read.
That sounds reasonable (these are older, slower machines). I would
have assumed that pvfs2-cp would have two buffers so that it can
read into one while sending the other.
The second image shows one of the 25 bulk IO transfers. There is
a 11 msec delay from the last send completing to the recv
completing (the large blue box). On the very far left is the
initial sendunexpected that starts this operation.
<pvfs2-cp-2.png>
So this 11 msec delay could be caused by writing to disk, but if
you don't have data sync enabled (which I don't think you do),
then 11 msec for 1 MB is about 90MB/s to write data to buffer
cache and return the write ack response. We might be delayed here
by having to wait for flow buffers being free'd up from one of the
first 8 1MB messages. Could you increase the FlowBuffersPerFlow
option in the fs.conf to 16 or 20 and see what happens?
-sam
I will try this.
I know that the default for FlowBuffersPerFlow is 8 per the
webpage, but I count 10 per flow in the log. I also find that when
using the -b flag, that it performs best with multiples of 10 buffers.
You're doing 10MB requests with 1MB flow buffers. I think the 10
flows per request are from that, so the number of flow buffers is
still 8, it just has to reuse 2 of them.
-b specifies the request size doesn't it? Using multiples of 10 for
that value improves performance? I really have no idea, but would
have guessed that multiples of the flow buffer size (in your case
1MB) would have been better.
-sam
Scott
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