Hi!
----
I'm getting a warning from "clang" when building ast-ksh.2013-04-09
related to sfio's |mmap()| I/O support:
-- snip --
src/lib/libast/sfio/sfmode.c:408:45: warning: comparison of constant
4096 with expression of type 'unsigned char'
is always false [-Wtautological-constant-out-of-range-compare]
if((f->bits&SF_MMAP) && (f->tiny[0] += 1) >= (4*SF_NMAP) )
~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~
1 warning generated.
-- snip --
The related code looks like this:
-- snip --
407 #if _mmap_worthy
408 if((f->bits&SF_MMAP) && (f->tiny[0] += 1) >=
(4*SF_NMAP) )
409 { /* turn off mmap to avoid page faulting */
410 sfsetbuf(f,(Void_t*)f->tiny,(size_t)SF_UNBOUND);
411 f->tiny[0] = 0;
412 }
413 else
414 #endif
-- snip --
... AFAIK we had that kind of warning for that line before.
AFAIK the code should turn-off |mmap()'ing of files if more than
(4*SF_NMAP) random accesses are made... right ?
However... I think the code has become useless:
1. The code was written _long_ ago and newer disks (not even counting
RAID configurations or SSD) have 4k block size (matching |(4*SF_NMAP)|
on AMD64/64bit) ... rendering the check more or less defunct since
even random file accesses via |read()| will fetch 4k blocks anyway
2. We always disabled that check in the OpenSolaris ksh93-integration
project because benchmarking showed that this check usually hurt ksh93
I/O performance by a few percent if it kicked-in (which only happned
for 32bit builds (for the same reason as above...))
----
Bye,
Roland
--
__ . . __
(o.\ \/ /.o) [email protected]
\__\/\/__/ MPEG specialist, C&&JAVA&&Sun&&Unix programmer
/O /==\ O\ TEL +49 641 3992797
(;O/ \/ \O;)
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