From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@armlinux.org.uk (Russell King - ARM Linux) Date: Fri, 21 Jul 2017 00:53:54 +0100 Subject: IMX53 on recent 4.4.x kernels In-Reply-To: References: <20170720123933.rioxhsthaaby4cnl@pengutronix.de> <20170720141528.kxrw5r4hpa2hebvd@pengutronix.de> Message-ID: <20170720235354.GF31807@n2100.armlinux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Jul 20, 2017 at 03:06:27PM +0000, Vellemans, Noel wrote: > 3.b: stripped ROOTFS to minimum on BOTH ( running the same STRIPPED rootfs) > And I did build a small TEST-tool that was probing for kernel time ( looping X times) as test result of this small test tool , I measured execution times on both Kernels ( it's a simple stupid loop probing for kernel time in a loop) > > The measured RUNTIMES on 2.6.35 are in the 18000 ms range > The measured RUNTIMES on 4.4.x are in the 61000 ms range ( see below) { for the same TEST tool } It may help to test some intervening kernels - v2.6.35 was released on 1st August 2010 and 4.4 in January 2016. That's an awful lot of changes, and to ask people what happened during six years to cause a performance regression is a tad unfair. I'd suggest one potential candidate for testing would be 2.6.38, where the clock_gettime() code was restructured somewhat - that shouldn't be too different from 2.6.35 to port your additional patches to. You may also like to consider doing a manual bisection of kernel versions to try and track down whether it's been a gradual loss of performance or a sudden change, and where it occurred. I know it's a pain to do it over such a large series of kernels, but otherwise you're basically asking people to guess. Also, I suspect most people's userspace may break if they try to wind their kernels back to 2.6.35 (I suspect most folk's hardware wasn't supported by that kernel.) Another thing to check is that you have features like the spinlock debug, semaphore debug, lockdep, tracing etc all disabled - these can add quite a bit of additional processing into critical paths. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.