From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Mosberger Date: Fri, 14 Mar 2003 19:46:50 +0000 Subject: Re: [Linux-ia64] Single bundle loops on Itanium-2 sometimes run slow Message-Id: List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org >>>>> On Fri, 14 Mar 2003 12:51:43 -0600 (CST), Jack Steiner said: Jack> SUMMARY: It appears that if a single bundle misaligned loop is Jack> interrupted (timer, etc), when the loop is resumed, it Jack> sometimes runs at about 1/3 the normal rate until the loop Jack> completes. (I dont mean 1 or a few iterations of the loop!!) Jack> 4000000000000eb0: [MIB] adds r8=1,r32 Jack> 4000000000000eb6: adds r32=-1,r32 4000000000000ebc: Jack> br.cloop.sptk.few 4000000000000eb0 ;; Jack> If "noise" is present, pfmon shows significant lost cycles due Jack> to BE_LOST_BW_DUE_TO_FE_BR_ILOCK. A 15 second sample shows: Jack> BE_LOST_BW_DUE_TO_FE_BR_ILOCK = 423 for good run Jack> BE_LOST_BW_DUE_TO_FE_BR_ILOCK = 105935651 for noisy run Jack> Changing the test so that code is at different addresses Jack> effects the likelyhood that noise will occur. Sometimes noise Jack> occurs on only a subset of the cpus. Sometimes booting a Jack> different kernel changes the likelyhood of seeing noise. Jack> Has anyone seen this behavior or have an explanation. Can you check whether the problem goes away when you turn the loop into a 2-cycle loop? My bet is that it will. --david