From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Helgaas Date: Fri, 27 Jan 2006 21:03:27 +0000 Subject: boot-time slowdown for measure_migration_cost Message-Id: <200601271403.27065.bjorn.helgaas@hp.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ingo Molnar Cc: linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org The boot-time migration cost auto-tuning stuff seems to have been merged to Linus' tree since 2.6.15. On little one- or two-processor systems, the time required to measure the migration costs isn't very noticeable, but by the time we get to even a four-processor ia64 box, it adds about 30 seconds to the boot time, which seems like a lot. Is that expected? Is the information we get really worth that much? Could the measurement be done at run-time instead? Is there a smaller hammer we could use, e.g., flushing just the buffer rather than the *entire* cache? Did we just implement sched_cacheflush() incorrectly for ia64? Only ia64, x86, and x86_64 currently have a non-empty sched_cacheflush(), and the x86* ones contain only "wbinvd()". So I suspect that only ia64 sees this slowdown. But I would guess that other arches will implement it in the future. Bjorn