From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Mon, 24 Aug 2015 16:00:31 +0100 Subject: [PATCH 0/4] Efficiency cleanups In-Reply-To: <20150824143619.GD20147@arm.com> References: <20150821133043.GV7557@n2100.arm.linux.org.uk> <20150821134630.GW7557@n2100.arm.linux.org.uk> <20150824143619.GD20147@arm.com> Message-ID: <20150824150031.GC7557@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Aug 24, 2015 at 03:36:20PM +0100, Will Deacon wrote: > On Fri, Aug 21, 2015 at 02:46:30PM +0100, Russell King - ARM Linux wrote: > > While developing the previous patch set, I noticed that the kernel's > > "fast" exit path efficiency was not what it's supposed to be due to the > > addition of trace and context tracking. > > > > These add several instances of register stacking and unstacking around > > various function calls, several of which we can avoid. Many of these > > instances don't need to stack any register other than r0. > > > > Moreover, we can avoid stacking and unstacking r0 if these features are > > enabled by storing r0 in the pt_regs as we would do in our slow return > > path. > > > > Various other cleanups are included in this set as well. Acks welcome. > > All four patches look fine to me: > > Acked-by: Will Deacon > > For some reason, I thought the numbering of the TIF_ flags was important > for some immediate construction in asm code, but either I'm mistaken or > it's no longer the case. The only reason they're important is to ensure that the bits are close enough together - we use the definitions directly in the asm code. Over the years, I think we've deleted a number of flags, and grown some others, and we've left holes in the bit allocation. By compressing them, we can change the assembly code to check for "is there _any_ work at all that needs to be done" as opposed to the two-step approach we've been doing up to now. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.