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Date:      Tue, 8 Dec 2015 22:54:50 +0000 (GMT)
From:      jenkins-admin@FreeBSD.org
To:        hiren@FreeBSD.org, andrew@FreeBSD.org, bdrewery@FreeBSD.org,  jenkins-admin@FreeBSD.org, freebsd-arm@FreeBSD.org
Subject:   FreeBSD_HEAD_arm64 - Build #1855 - Fixed
Message-ID:  <1895771148.7.1449615292061.JavaMail.jenkins@jenkins-9.freebsd.org>
In-Reply-To: <1528023525.5.1449607772519.JavaMail.jenkins@jenkins-9.freebsd.org>
References:  <1528023525.5.1449607772519.JavaMail.jenkins@jenkins-9.freebsd.org>

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FreeBSD_HEAD_arm64 - Build #1855 - Fixed:

Build information: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/1855/
Full change log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/1855/changes
Full build log: https://jenkins.FreeBSD.org/job/FreeBSD_HEAD_arm64/1855/console

Change summaries:

292003 by hiren:
One of the ways to detect loss is to count duplicate acks coming back from the
other end till it reaches predetermined threshold which is 3 for us right now.
Once that happens, we trigger fast-retransmit to do loss recovery.

Main problem with the current implementation is that we don't honor SACK
information well to detect whether an incoming ack is a dupack or not. RFC6675
has latest recommendations for that. According to it, dupack is a segment that
arrives carrying a SACK block that identifies previously unknown information
between snd_una and snd_max even if it carries new data, changes the advertised
window, or moves the cumulative acknowledgment point.

With the prevalence of Selective ACK (SACK) these days, improper handling can
lead to delayed loss recovery.

With the fix, new behavior looks like following:

0) th_ack < snd_una --> ignore
Old acks are ignored.
1) th_ack == snd_una, !sack_changed --> ignore
Acks with SACK enabled but without any new SACK info in them are ignored.
2) th_ack == snd_una, window == old_window --> increment
Increment on a good dupack.
3) th_ack == snd_una, window != old_window, sack_changed --> increment
When SACK enabled, it's okay to have advertized window changed if the ack has
new SACK info.
4) th_ack > snd_una --> reset to 0
Reset to 0 when left edge moves.
5) th_ack > snd_una, sack_changed --> increment
Increment if left edge moves but there is new SACK info.

Here, sack_changed is the indicator that incoming ack has previously unknown
SACK info in it.

Note: This fix is not fully compliant to RFC6675. That may require a few
changes to current implementation in order to keep per-sackhole dupack counter
and change to the way we mark/handle sack holes.

PR:			203663
Reviewed by:		jtl
MFC after:		3 weeks
Sponsored by:		Limelight Networks
Differential Revision:	https://reviews.freebsd.org/D4225

292002 by bdrewery:
CCACHE_BUILD: Only export CCACHE_PATH= if it was already set with a value.

Older ccache don't work with an empty CCACHE_PATH value.  They will error with:
  ccache: FATAL: Could not find compiler "cc" in PATH
  make: "/mnt/bdrewery/git/onefs/src/share/mk/bsd.compiler.mk" line 134: Unable to determine compiler type for /usr/local/bin/ccache cc.  Consider setting COMPILER_TYPE.

Sponsored by:	EMC / Isilon Storage Division

292001 by andrew:
ahci_generic.c needs ofw_bus_if.h, add it to the module.




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