Messages in this thread | | | Date | Wed, 15 Jun 2022 14:44:29 -0400 | Subject | Re: [PATCH v3 03/33] vsprintf: Convert to printbuf | From | Kent Overstreet <> |
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On 6/15/22 05:09, Rasmus Villemoes wrote: > On 04/06/2022 21.30, Kent Overstreet wrote: >> This converts vsnprintf() to printbufs: instead of passing around raw >> char * pointers for current buf position and end of buf, we have a real >> type! >> >> This makes the calling convention for our existing pretty printers a lot >> saner and less error prone, plus printbufs add some new helpers that >> make the code smaller and more readable, with a lot less crazy pointer >> arithmetic. >> >> There are a lot more refactorings to be done: this patch tries to stick >> to just converting the calling conventions, as that needs to be done all >> at once in order to avoid introducing a ton of wrappers that will just >> be deleted. >> >> Thankfully we have good unit tests for printf, and they have been run >> and are all passing with this patch. > > So, as the primary author of those tests, a somewhat active contributor > to vsprintf.c and being listed as R: for both files, why wasn't I cc'ed > on this?
Apologies for the oversight.
> Anyway, my main concern with this is that performance goes down the > drain and the generated code will be awful. Have you done any > measurements and/or looked at disassembly? Thanks to > -fno-strict-aliasing (or perhaps just because we're writing through a > char* pointer which IIRC may alias anything), I think the compiler will > be forced to reload prt->pos and prt->size over and over and over. I may > be wrong, of course, that happens often. Perhaps __restrict could help, IDK.
If we care that much about sprintf performance we must have some benchmarks somewhere - could you point me at them?
>> --- >> include/linux/kernel.h | 4 + > > Please don't expand that dumping ground. Please, if printbufs will > become a thing (whether or not vsprintf internally will be refactored to > use them), add a new linux/printf.h where these things can go, and the > declarations of vsprintf() and close friends can eventually be moved.
kernel.h is indeed a dumping ground that needs to be reorganized, but this patch series is about printbufs, not reorganizing header files (and my doctor tells me I need to be taking my blood pressure meds more regularly before taking something like that on). For now, prt_printf() goes with the other printf() functions.
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