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Message-ID: <m1lj842nph.fsf@fess.ebiederm.org> Date: Wed, 18 Aug 2010 03:56:58 -0700 From: ebiederm@...ssion.com (Eric W. Biederman) To: "Zhang\, Yanmin" <yanmin_zhang@...ux.intel.com> Cc: LKML <linux-kernel@...r.kernel.org>, alex.shi@...el.com, Pavel Emelyanov <xemul@...nvz.org>, "David S. Miller" <davem@...emloft.net> Subject: Re: hackbench regression with 2.6.36-rc1 "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com> writes: > Comparing with 2.6.35's result, hackbench (thread mode) has about > 80% regression on dual-socket Nehalem machine and about 90% regression > on 4-socket Tigerton machines. That seems unfortunate. Do you only show a regression in the pthread hackbench test? Do you show a regression when you use pipes? Does the size of the regression very based on the number of loop iterations? I ask because it appears that on the last message the sender will exit necessitating that the receiver put the senders pid. Which should be atypical. > Command to start hackbench: > #./hackbench 100 thread 2000 > > process mode has no such regression. > > Profiling shows: > #perf top > samples pcnt function DSO > _______ _____ ________________________ ________________________ > > 74415.00 29.9% put_pid [kernel.kallsyms] > 38395.00 15.4% unix_stream_recvmsg [kernel.kallsyms] > 34877.00 14.0% unix_stream_sendmsg [kernel.kallsyms] > 25204.00 10.1% pid_vnr [kernel.kallsyms] > 21864.00 8.8% unix_scm_to_skb [kernel.kallsyms] > 13637.00 5.5% cred_to_ucred [kernel.kallsyms] > 6520.00 2.6% unix_destruct_scm [kernel.kallsyms] > 4731.00 1.9% sock_alloc_send_pskb [kernel.kallsyms] > > > With 2.6.35, perf doesn't show put_pid/pid_NR. Yes. 2.6.35 is imperfect and can report the wrong pid in some circumstances. I am surprised nothing related to the reference count on struct cred does not show up in your profiling traces. You are performing statistical sampling so I don't believe the percentage of hits per function is the same as the percentage of time per function. Given that we are talking about a scheduler benchmark that is doing something rather artificial (inter thread communication via sockets), I don't know that this case is worth worrying about. > Alex Shi and I did a quick bisect and located below 2 patches. That is a plausible result. The atomic reference counts may be causing you to ping pong cache lines between cpus. Eric > 1) commit 7361c36c5224519b258219fe3d0e8abc865d8134 > Author: Eric W. Biederman <ebiederm@...ssion.com> > Date: Sun Jun 13 03:34:33 2010 +0000 > > af_unix: Allow credentials to work across user and pid namespaces. > > In unix_skb_parms store pointers to struct pid and struct cred instead > of raw uid, gid, and pid values, then translate the credentials on > reception into values that are meaningful in the receiving processes > namespaces. > > > 2) commit 257b5358b32f17e0603b6ff57b13610b0e02348f > Author: Eric W. Biederman <ebiederm@...ssion.com> > Date: Sun Jun 13 03:32:34 2010 +0000 > > scm: Capture the full credentials of the scm sender. > > Start capturing not only the userspace pid, uid and gid values of the > sending process but also the struct pid and struct cred of the sending > process as well. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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