On Tuesday, November 18, 2014 10:55:31 PM UTC-8, Uli wrote: > > >>> Lee Duncan <leeman...@gmail.com <javascript:>> schrieb am 18.11.2014 > um 22:35 in > Nachricht <1416346536-18198-1-git-seemail-###-duncan@ <javascript:>###>: > > The following patch fixes a problem where the CPU becomes compute bound > > when rediscovering targets, when there are hundreds of sessions. > > > > When his occurs, most of the time is spent in the function > > iscsi_sysfs_for_each_session(). This function does a scandir(), > > sorted alphabetically, to get a list of sessions, then scans > > that list looking for a match. When there are hundreds of sesions > > this can take forever. > > > I wonder: What takes forever: reading hundreds of sysfs entries, sorting > them, or looking for a match? I guess none of them should take forever > unless the algorithm is really very bad. >
The problem is not the sort, since the patch still does a sort of the directory entries. I believe the problem is in processing the sorted data, in iscsi_sysfs_for_each_session(). This function does dozens or more open/read/close cycles on sysfs attributes. Multiply that times hundreds of session, and you have tens of thousands I/O operations. This fix ensures that, much of time, this loop is only gone through once. > > > > This patch saves the current session and then ensures that this > > session sorted to the front of the list. Testing shows that > > CPU usage goes from near 100% to near 0% when running cable > > plug tests with hundreds of sessions. > > > > Signed-off-by: Lee Duncan <leeman...@gmail.com <javascript:>> > > > > -- > > You received this message because you are subscribed to the Google > Groups > > "open-iscsi" group. > > To unsubscribe from this group and stop receiving emails from it, send > an > > email to open-iscsi+...@googlegroups.com <javascript:>. > > To post to this group, send email to open-...@googlegroups.com > <javascript:>. > > Visit this group at http://groups.google.com/group/open-iscsi. > > For more options, visit https://groups.google.com/d/optout. > > > > > -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to open-iscsi+unsubscr...@googlegroups.com. To post to this group, send email to open-iscsi@googlegroups.com. Visit this group at http://groups.google.com/group/open-iscsi. For more options, visit https://groups.google.com/d/optout.
