Date: Thu, 10 Apr 2003 13:11:43 -0700 From: Sean Chittenden <sean@chittenden.org> To: "Jin Guojun [NCS]" <j_guojun@lbl.gov> Cc: freebsd-performance@freebsd.org Subject: Re: tcp_output starving -- is due to mbuf get delay? Message-ID: <20030410201143.GF79923@perrin.int.nxad.com> In-Reply-To: <3E95BEBB.58F86F4F@lbl.gov> References: <3E94A22D.174321F0@lbl.gov> <20030409230733.GX79923@perrin.int.nxad.com> <3E94B993.D282DEB2@lbl.gov> <20030410005846.GA79923@perrin.int.nxad.com> <3E95A37E.36186A9F@lbl.gov> <3E95A653.8F5CE89C@lbl.gov> <3E95BEBB.58F86F4F@lbl.gov>
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> I guess I overlooked something after applying the patch (attached): > > Apr 10 12:11:52 ncs /kernel: sbappend: bad tail 0x0xc209a200 instead of 0x0xc243 > 6c00 > Apr 10 12:11:52 ncs /kernel: sbappend: bad tail 0x0xc2436c00 instead of 0x0xc238 > bf00 > Apr 10 12:11:52 ncs /kernel: sbappend: bad tail 0x0xc238bf00 instead of 0x0xc243 > f300 > ... > > A large number of such message was added into /var/log/message. This > indicates either bad patch code or something I changed in the patch > to make it work in 4.8 (attached). > > Any thought? That's likely the sign that the patch isn't appending to the tail of the list correctly. Doing a tail append where the tail is known should be an O(1) operation and should make adding an mbuf to a cluster faster. Right now it has to do a linear scan to append data, iirc, which is likely _a_ cause of some performance degradation. I'm not an mbuf expert, but I wonder how free mbuf's are identified. Regardless, I'll see if I can't figure out where this problem is with the patch, it should do nothing but make things faster. -sc -- Sean Chittenden
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