On Thu, Feb 18, 2021 at 05:15:43PM +0200, Andy Shevchenko wrote: > On Wed, Feb 17, 2021 at 08:05:06PM -0800, Yury Norov wrote: > > This series introduces fast paths for find_bit() routines. It is > > beneficial for typical systems, but those who limited in I-cache > > may be concerned about increasing the .text size of the Image. > > > > To address this concern, one can disable FAST_PATH option in the config > > and some save memory. > > > > The effect of this option on my arm64 next-20210217 build is: > > (Maybe bloat-o-meter will give better view on this, i.e. more human-readable)
Never heard about this tool, thanks for the hint. scripts/bloat-o-meter vmlinux vmlinux.new add/remove: 16/13 grow/shrink: 111/439 up/down: 3616/-19352 (-15736) Function old new delta find_next_bit.constprop - 220 +220 apply_wqattrs_cleanup - 176 +176 memcg_free_shrinker_maps - 172 +172 ... cpuset_hotplug_workfn 2584 2288 -296 task_numa_fault 3640 3320 -320 kmem_cache_free_bulk 1684 1280 -404 Total: Before=26085140, After=26069404, chg -0.06% The complete output is here: https://pastebin.com/kBSdVJcK So if I understand the output correctly, the size of .text is decreased... Looks weird, but if it's true, we don't need the FAST_BIT config at all because there's no tradeoff, and I should drop the patch. Hmm... > > +config FAST_PATH > > I think the name is to broad for this cases, perhaps BITS_FAST_PATH? or > BITMAP? My logic was that since SMALL_CONST() is global, and FAST_PATH controls the SMALL_CONST, it should also be global. I believe, Linux should have a global switch to control the behaviour in such cases, similarly to -Os compiler option. And I was surprized when I found nothing like FAST_PATH in the config. What about having FAST_PATH as a global option, and later if someone will request for granularity, we'll introduce nested configs? > > + bool "Enable fast path code generation" > > + default y > > + help > > + This option enables fast path optimization with the cost of increasing > > + the text section. > > -- > With Best Regards, > Andy Shevchenko >
