Question about BITSET_WORD
Hi, I'm new to this list, so sorry if it is not the correct place. I've started to looked at the source code of mesa and I wonder why in src/util/bitset.h we have: #define BITSET_WORD unsigned int This is as-is since at least 2015, probably 2011. Would it make sense to have it as a long, at least on 64 bits arch? (the linux kernel uses bitmaps as unsigned long) I don't think that it should be a noticeable speed-up, but at least on Linux it could save some cycles when doing some OR or AND and co on bitmaps on a 64 bits cpu. Just my 2c. Christophe JAILLET
Re: Question about BITSET_WORD
I've actually benchmarked this and 32bit is still faster on many modern CPUs. Also, I would be very surprised if we could change it without breaking the universe. I'm sure there are hard-coded 32s various places. ~Faith On Wed, Aug 21, 2024 at 8:13 AM Christophe JAILLET < christophe.jail...@wanadoo.fr> wrote: > Hi, > > I'm new to this list, so sorry if it is not the correct place. > > I've started to looked at the source code of mesa and I wonder why in > src/util/bitset.h we have: > > #define BITSET_WORD unsigned int > > This is as-is since at least 2015, probably 2011. > > Would it make sense to have it as a long, at least on 64 bits arch? > (the linux kernel uses bitmaps as unsigned long) > > I don't think that it should be a noticeable speed-up, but at least on > Linux it could save some cycles when doing some OR or AND and co on > bitmaps on a 64 bits cpu. > > Just my 2c. > > Christophe JAILLET >
Re: Question about BITSET_WORD
Maybe there should be a comment regarding the performance and risk of change? -Brian On 8/21/24 07:54, Faith Ekstrand wrote: I've actually benchmarked this and 32bit is still faster on many modern CPUs. Also, I would be very surprised if we could change it without breaking the universe. I'm sure there are hard-coded 32s various places. ~Faith On Wed, Aug 21, 2024 at 8:13 AM Christophe JAILLET wrote: Hi, I'm new to this list, so sorry if it is not the correct place. I've started to looked at the source code of mesa and I wonder why in src/util/bitset.h we have: #define BITSET_WORD unsigned int This is as-is since at least 2015, probably 2011. Would it make sense to have it as a long, at least on 64 bits arch? (the linux kernel uses bitmaps as unsigned long) I don't think that it should be a noticeable speed-up, but at least on Linux it could save some cycles when doing some OR or AND and co on bitmaps on a 64 bits cpu. Just my 2c. Christophe JAILLET -- This electronic communication and the information and any files transmitted with it, or attached to it, are confidential and are intended solely for the use of the individual or entity to whom it is addressed and may contain information that is confidential, legally privileged, protected by privacy laws, or otherwise restricted from disclosure to anyone else. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, you are hereby notified that any use, copying, distributing, dissemination, forwarding, printing, or copying of this e-mail is strictly prohibited. If you received this e-mail in error, please return the e-mail to the sender, delete it from your computer, and destroy any printed copy of it.
Re: Question about BITSET_WORD
All 32-bit operations are generally faster than 64-bit. If both happen to have the same performance per clock (that would have to be a deliberate hw design choice), 32-bit opcodes have likely lower power consumption, which allows a higher core frequency. That doesn't even scratch the surface. Explaining exactly why some instructions are faster or slower would require detailed hw specs. Marek On Wed, Aug 21, 2024 at 10:05 AM Faith Ekstrand wrote: > > I've actually benchmarked this and 32bit is still faster on many modern CPUs. > > Also, I would be very surprised if we could change it without breaking the > universe. I'm sure there are hard-coded 32s various places. > > ~Faith > > On Wed, Aug 21, 2024 at 8:13 AM Christophe JAILLET > wrote: >> >> Hi, >> >> I'm new to this list, so sorry if it is not the correct place. >> >> I've started to looked at the source code of mesa and I wonder why in >> src/util/bitset.h we have: >> >> #define BITSET_WORD unsigned int >> >> This is as-is since at least 2015, probably 2011. >> >> Would it make sense to have it as a long, at least on 64 bits arch? >> (the linux kernel uses bitmaps as unsigned long) >> >> I don't think that it should be a noticeable speed-up, but at least on >> Linux it could save some cycles when doing some OR or AND and co on >> bitmaps on a 64 bits cpu. >> >> Just my 2c. >> >> Christophe JAILLET
