[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: File System Performance Loss in Genera 8.0 (16X slower!)

	Date: Fri, 6 Jul 90 16:20 EDT
	From: barmar@Think.COM (Barry Margolin)
	Subject: File System Performance Loss in Genera 8.0 (16X slower!)
	To: cogen@XN.LL.MIT.EDU
	cc: SLUG@Warbucks.AI.SRI.COM

	Another change that can affect things adversely is the support in 8.0
	IP-TCP for reassembling large datagrams, which is used by 8.0 NFS.
	The maximum packet size on an ethernet is about 1500 bytes, but NFS
	will request 8Kbytes of the file at a time.  This datagram will be
	split into a series of ethernet packets, but if just one of them isn't
	received the entire series will have to be sent again (retransmission
	occurs at the datagram level, not the packet level).  I was seeing
	this when I was trying my above "benchmarks" on another machine (go
	into Peek Network mode and check whether there are a bunch of
	Reassembly Nodes -- this indicates you're getting lots of partial

Yes!  We are seeing precisely the same thing.  Attempts to access an
Ultrix system via NFS using Rel.8 will often result in long delays.
Peek Network shows many Reassembly Nodes.   Can you elaborate on
what 8.0 is doing differently regarding the reassembly of large
packets?  Did something different happen in 7.2 (where we never
had this problem)?  Does anybody have a cure for this?