shoshana@pdi.UUCP (Shoshana Abrass) (05/24/91)
We're thinking of tuning the buffer cache to speed disk i/o. We often have to read two large files alternately (for example, a geometry model, then a texture map, then the model, then the map, etc...) and we'd like to keep both (or many) of these files in the cache, if possible. (Yes, we're looking at alternate schemes, but this is a fast hack. The two files are read by separate processes that exit after reading, BTW.) The 'documentation' in /usr/sysgen/master.d/master.c says #define NBUF 0 /* # buffers in disk buffer cache */ /* autoconfigure if 0 */ What does 'autoconfigure' mean? does this configure when you compile the kernel, or does it dynamically change depending on what your file usage profile is? And what's a real number that I can set this to, or how can I find out what it's autoconfigured to now? And while I'm on the subject.... Someone at my company is strongly of the belief that MIPS-based operating systems have the capability of running a RAM disk. Without flaming about the viability of this solution, can anyone confirm or deny it? Thanks for any help. -shoshana shoshana@pdi.com pdi!shoshana@sgi.com ...uunet!sgi!pdi!shoshana --
jeremy@perf2.asd.sgi.com (Jeremy Higdon) (05/25/91)
In article <9105240159.AA10726@koko.pdi.com>, shoshana@pdi.UUCP (Shoshana Abrass) writes: > > We're thinking of tuning the buffer cache to speed disk i/o. > We often have to read two large files alternately (for example, > a geometry model, then a texture map, then the model, then the > map, etc...) and we'd like to keep both (or many) of these > files in the cache, if possible. (Yes, we're looking at alternate > schemes, but this is a fast hack. The two files are read by > separate processes that exit after reading, BTW.) > > The 'documentation' in /usr/sysgen/master.d/master.c says > > #define NBUF 0 /* # buffers in disk buffer cache */ > /* autoconfigure if 0 */ > > What does 'autoconfigure' mean? does this configure when you > compile the kernel, or does it dynamically change depending on > what your file usage profile is? And what's a real number that > I can set this to, or how can I find out what it's autoconfigured > to now? In IRIX 3.3 and beyond, cached file data does not use a buffer header. Thus, if you have enough memory, your files will stay cached automatically. Basically, whatever isn't in use by the kernel, user programs, etc. is available for caching disk files. Currently, autoconfiguring for the number of buffers is done at boot time and depends on the amount of memory on your machine. If I remember correctly, it is 50 + (25 per 8MB).