Messages in this thread | | | Date | Tue, 21 Feb 2017 15:49:34 +0000 | From | Will Deacon <> | Subject | Re: [PATCH v2] arm64: cache: Skip an unnecessary data cache clean PoU operation |
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On Tue, Feb 21, 2017 at 03:47:27PM +0000, Catalin Marinas wrote: > On Wed, Feb 08, 2017 at 03:19:37PM -0600, Shanker Donthineni wrote: > > The cache management functions always do the data cache PoU > > (point of unification) operations even though it is not required > > on some systems. No need to clean data cache till PoU if all the > > cache levels below PoUIS are WT (Write-Through) caches. It causes > > a huge performance degradation when operating on a larger memory > > area, especially THP with 64K page size kernel. > > > > For each online CPU, check the need of 'dc cvau' instruction and > > update a global variable __dcache_flags. The two functions > > __flush_cache_user_range() and __clean_dcache_area_pou() are > > modified to skip an unnecessary code execution based on flags. > > It won't change the existing behavior if any one of the online > > CPU is capable of WB cache below PoUIS level. > > > > Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org> > [...] > > +#define CLIDR_LOUIS_SHIFT (21) > > +#define CLIDR_LOUIS_MASK (0x7) > > +#define CLIDR_LOUIS(x) (((x) >> CLIDR_LOUIS_SHIFT) & CLIDR_LOUIS_MASK) > > According to the ARMv8 ARM, CLIDR_EL1 "identifies the type of cache, or > caches, that are implemented at each level and can be managed using the > architected cache maintenance instructions that operate by set/way". The > key part is "set/way" here and hence you cannot use CLIDR_EL1 and > CCSIDR_EL1 to infer whether you can skip cache maintenance by VA. > > > + /* Go through all the cache level below LoUIS */ > > + for (lvl = 0; lvl < louis; lvl++) { > > + csidr = cache_get_ccsidr(lvl << 1); > > + if (csidr & CCSIDR_EL1_WRITE_BACK) { > > The type bits have also been deprecated in ARMv8 (we need to update the > kernel or just remove the cache topology detection entirely, leaving it > just to DT).
I'll dust off the patches I have for this...
Will
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