-----Original Message----- From: U-Boot u-boot-bounces@lists.denx.de On Behalf Of Rasmus Villemoes Sent: Friday, September 18, 2020 1:51 PM To: Stefan Roese sr@denx.de; u-boot@lists.denx.de Cc: Christophe Leroy christophe.leroy@c-s.fr; Wolfgang Denk wd@denx.de; Simon Glass sjg@chromium.org; Tom Rini trini@konsulko.com Subject: Re: [PATCH] powerpc: reduce number of WATCHDOG_RESET calls from flush_cache
On 04/06/2020 12.31, Stefan Roese wrote:
On 04.06.20 11:30, Rasmus Villemoes wrote:
Calling WATCHDOG_RESET for each and every cache line is overkill.
In our case, the kernel image is a little over 7MB, and the almost 500000 calls of WATCHDOG_RESET() adds about one second to the boottime.
I very highly doubt there's any real hardware where flushing 64K from cache to memory takes more than a few milliseconds, so this should be completely safe. Since it reduces the number of WATCHDOG_RESET() calls by roughly a factor of 1000, the overhead from those is practically eliminated. (Just in case the range flushed is so small that it doesn't cross a 64K boundary, add a single WATCHDOG_RESET() between the loops).
64K is chosen because that's also the default chunk size used by the hashing algorithms, and when, say, a sha256 digest of a kernel image of a few MB is being verified, that's almost guaranteed to be cache-cold, so apart from the computations being done, the hashing is also bounded by memory speed - so if 64K works for those cases, it should certainly also work when memory access is the only thing being
done.
Signed-off-by: Rasmus Villemoes rasmus.villemoes@prevas.dk
Reviewed-by: Stefan Roese sr@denx.de
<snip> Applied to u-boot-mpc85xx. Awaiting upstream
Thanks Priyanka