From: Peter Oberparleiter Date: Tue, 26 Nov 2013 13:55:56 +0000 (+0100) Subject: s390/cio: More efficient handling of CHPID availability events X-Git-Tag: v3.14-rc1~184^2~43 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=449666dd1efacaf3f0eb020cc617dd702356575c;p=pandora-kernel.git s390/cio: More efficient handling of CHPID availability events The CIO layer processes hardware events that indicate that a channel path has become available by performing a scan of available subchannels using the Store Subchannel (STSCH) instruction. Performing too many STSCH instructions in a tight loop can cause high Hypervisor overhead which can negatively impact the performance of the virtual machine as a whole. This patch reduces the number of STSCH instructions performed while processing a resource accessibility event and while varying a CHPID online. In both cases, Linux first performs a STSCH instruction on each unused subchannel to see if the subchannel has become available. If the STSCH instruction indicates that the subchannel is available, a full evaluation of this subchannel is scheduled. Since the full evaluation includes performing a STSCH instruction, the initial STSCH is unnecessary and can be removed. Signed-off-by: Peter Oberparleiter Reviewed-by: Sebastian Ott Signed-off-by: Martin Schwidefsky --- Reading git-diff-tree failed