On Friday 06 October 2006 06:51, Vadim Lobanov wrote:
> - nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1));
> - if (nfds > NR_OPEN)
> - nfds = NR_OPEN;
> -
> - new_openset = alloc_fdset(nfds);
> - new_execset = alloc_fdset(nfds);
> - if (!new_openset || !new_execset)
> - goto out;
> - fdt->open_fds = new_openset;
> - fdt->close_on_exec = new_execset;
> - fdt->max_fdset = nfds;
> -
> nfds = NR_OPEN_DEFAULT;
> /*
> * Expand to the max in easy steps, and keep expanding it until
> @@ -271,15 +254,21 @@ static struct fdtable *alloc_fdtable(int
> nfds = NR_OPEN;
> }
> } while (nfds <= nr);
If I understand well, we may allocate very small fdset, while previous minimum
size was L1_CACHE_BYTES bytes. (512 bits for a 64 bytes cache line)
If you check commit 0c9e63fd38a2fb2181668a0cdd622a3c23cfd567,
(http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=0c9e63fd38a2fb2181668a0cdd622a3c23cfd567 )
you'll find this comment of mine :
3) Reduce size of allocated fdset. Currently two full pages are
allocated, that is 32768 bits on x86 for example, and way too much. The
minimum is now L1_CACHE_BYTES.
This minimum is mandatory to be sure two tasks wont share the same cache line
to store their fdset (and possibly do lot of cache line ping pongs)
Eric
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