Re: [PATCH 7/8] arm64: Better optimised memchr()
From: Robin Murphy <robin.murphy@arm.com>
Date: 2021-05-14 18:40:42
On 2021-05-14 15:55, Catalin Marinas wrote:
On Tue, May 11, 2021 at 05:12:37PM +0100, Robin Murphy wrote:quoted
Although we implement our own assembly version of memchr(), it turns out to be barely any better than what GCC can generate for the generic C version (and would go wrong if the size_t argument were ever large enough to be interpreted as negative). Unfortunately we can't import the tuned implementation from the Arm optimized-routines library, since that has some Advanced SIMD parts which are not really viable for general kernel library code. What we can do, however, is pep things up with some relatively straightforward word-at-a-time logic for larger calls. Adding some timing to optimized-routines' memchr() test for a simple benchmark, overall this version comes in around half as fast as the SIMD code, but still nearly 4x faster than our existing implementation. Signed-off-by: Robin Murphy <robin.murphy@arm.com>I haven't reviewed the code yet but wondering - could we write this in C using load_unaligned_zeropad()?
I've had a hack around with a couple of C implementations this afternoon, and they seem to come out roughly 85% as fast as this asm version. I'm not sure how much extra overhead load_unaligned_zeropad() would add with wiggling PSTATE.TCO all the time, though. Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel