On 6/4/23 5:38?PM, Kent Overstreet wrote: > On Tue, May 30, 2023 at 10:50:55AM -0600, Jens Axboe wrote: >> Sorry typo, I meant text. Just checked stack and it looks identical, but >> things like blk-map grows ~6% more text, and bio ~3%. Didn't check all >> of them, but at least those two are consistent across x86-64 and >> aarch64. Ditto on the data front. Need to take a closer look at where >> exactly that is coming from, and what that looks like. > > A good chunk of that is because I added warnings and assertions for > e.g. running past the end of the bvec array. These bugs are rare and > shouldn't happen with normal iterator usage (e.g. the bio_for_each_* > macros), but I'd like to keep them as a debug mode thing. > > But we don't yet have CONFIG_BLOCK_DEBUG - perhaps we should. Let's split those out then, especially as we don't have a BLOCK_DEBUG option right now. > With those out, I see a code size decrease in bio.c, which makes sense - > gcc ought to be able to generate slightly better code when it's dealing > with pure values, provided everything is inlined and there's no aliasing > considerations. > > Onto blk-map.c: > > bio_copy_kern_endio_read() increases in code size, but if I change > memcpy_from_bvec() to take the bvec by val instead of by ref it's > basically the same code size. There's no disadvantage to changing > memcpy_from_bvec() to pass by val. > > bio_copy_(to|from)_iter() is a wtf, though - gcc is now spilling the > constructed bvec to the stack; my best guess is it's a register pressure > thing (but we shouldn't be short registers here!). > > So, since the fastpath stuff in bio.c gets smaller and blk-map.c is not > exactly fastpath stuff I'm not inclined to fight with gcc on this one - > let me know if that works for you. > > Branch is updated - I split out the new assertions into a separate patch > that adds CONFIG_BLK_DEBUG, and another patch for mempcy_(to|from)_bio() > for a small code size decrease. > > https://evilpiepirate.org/git/bcachefs.git/log/?h=block-for-bcachefs > or > git pull http://evilpiepirate.org/git/bcachefs.git block-for-bcachefs Cn you resend just the iterator changes in their current form? The various re-exports are a separate discussion, I think we should focus on the iterator bits first. -- Jens Axboe
