Date: Wed, 21 Aug 2013 12:11:08 -0700 From: Navdeep Parhar <np@FreeBSD.org> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Please review: LRO entry last-active timestamp. Message-ID: <521510CC.3040104@FreeBSD.org>
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I'd like to add a last-active timestamp to the structure that tracks the LRO state in a NIC's rx handler. This is r254336 in user/np/cxl_tuning that will be merged to head if there are no objections. http://svnweb.freebsd.org/base?view=revision&revision=254336 http://svnweb.freebsd.org/base/user/np/cxl_tuning/sys/netinet/tcp_lro.c?r1=254336&r2=254335&pathrev=254336 http://svnweb.freebsd.org/base/user/np/cxl_tuning/sys/netinet/tcp_lro.h?r1=254336&r2=254335&pathrev=254336 ----- Add a last-modified timestamp to each LRO entry and provide an interface to flush all inactive entries. Drivers decide when to flush and what the inactivity threshold should be. Network drivers that process an rx queue to completion can enter a livelock type situation when the rate at which packets are received reaches equilibrium with the rate at which the rx thread is processing them. When this happens the final LRO flush (normally when the rx routine is done) does not occur. Pure ACKs and segments with total payload < 64K can get stuck in an LRO entry. Symptoms are that TCP tx-mostly connections' performance falls off a cliff during heavy, unrelated rx on the interface. Flushing only inactive LRO entries works better than any of these alternates that I tried: - don't LRO pure ACKs - flush _all_ LRO entries periodically (every 'x' microseconds or every 'y' descriptors) - stop rx processing in the driver periodically and schedule remaining work for later. ----- Regards, Navdeep
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