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Subjectdo_select() improvement ...

This patch can improve do_select() ==> select() performance due :

1) the load from the fd bitmap is done every __NFDBITS instead of every bit.
If You look at the BITS() macro You'll see that it's not cheap in terms
of memory operations

2) if a sequential hole of __NFDBITS is found it'll be skipped without doing a
bit by bit check




*** select.orig.c Thu Jun 21 08:52:04 2001
--- select.c Thu Jun 21 12:09:25 2001
***************
*** 164,171 ****
--- 164,172 ----
{
poll_table table, *wait;
int retval, i, off;
long __timeout = *timeout;
+ unsigned long bits;

read_lock(&current->files->file_lock);
retval = max_select_fd(n, fds);
read_unlock(&current->files->file_lock);
***************
*** 186,194 ****
unsigned long mask;
struct file *file;

off = i / __NFDBITS;
! if (!(bit & BITS(fds, off)))
continue;
file = fget(i);
mask = POLLNVAL;
if (file) {
--- 187,202 ----
unsigned long mask;
struct file *file;

off = i / __NFDBITS;
! if (!(i & (__NFDBITS - 1))) {
! bits = BITS(fds, off);
! if (!bits) {
! i += __NFDBITS;
! continue;
! }
! }
! if (!(bit & bits))
continue;
file = fget(i);
mask = POLLNVAL;
if (file) {







- Davide

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