On Wed, Nov 29, 2017 at 10:35:55AM +0100, Clement Courbet wrote: > > > Note that on Arm (), the new c implementation still outperforms the > > > old one that uses c+ the asm implementation of `find_next_bit` [3]. > > What is 'c+'? Is it typo? > > I meant "a mix of C and asm" ~(C + asm). Rephrased. > > > If you find generic find_bit() on arm faster that asm one, we'd > > definitely drop that piece of asm. I have this check it in my > > long list. > > What's faster for sure is the mix (the improvement in this commit minus the > possible hit from not using the ASM implementation). I can't tell whether the > latter is negligible or not (I only have one ARM board to try it out), but > that's definitly something to try. > > > This is old version of test based on get_cycles. New one is based on > > ktime_get and has other minor changes. I think you'd rerun tests to > > not confuse readers. New version is already in linux-next. > > So I'm not sure whether I should be submitting this against 'linux' or > 'linux-next' ? This patch is against 'linux', so I think it should > be consistent with the code around.
Linux-next is your choice. https://lwn.net/Articles/289013/ > > > #ifndef find_first_bit > > > #define find_first_bit(addr, size) find_next_bit((addr), (size), 0) > > > #endif > > > #ifndef find_first_zero_bit > > > #define find_first_zero_bit(addr, size) find_next_zero_bit((addr), > > > (size), 0) > > > #endif > > How this change related to the find_next_and_bit? > > The arm header defines these symbols. Now that we're including > the generic implementation in the arm headers, we need to guard this to > avoid the duplicate definition. So I think it really worth to be separated patch. Really, it's completely nontrivial why adding new function in lib/find_bit.c requires including asm-generic/bitops/find.h in arm and uncore32 asm/bitops.h headers (bug?). And why doing that makes you guard find_first_bit and find_first_zero_bit (another bug?). Headers are always important. Please elaborate it and also CC arm and uncore32 communities, linux-arch and Arnd Bergman. > > > test_find_next_and_bit_ref > > I don't understand the purpose of this. It's obviously clear that > > test_find_next_and_bit cannot be slower than test_find_next_and_bit_ref > > Fair enough :) That was to back my claim that this commit is worth it. > I've removed the "_ref" version. > > > For sparse bitmaps it will be like traversing zero-bitmaps. I doubt > > this numbers will be representative. Do we need this test at all? > > It's just two lines, and gives an interesting data point. Why not > keep it ? --- Again. test_find_next_and_bit is trimmed, but it is still based on get_cycles and uses tabs in printf(). Please fix it. Yury
