Date: Sun, 16 Feb 1997 16:04:02 +0300 (MSK) From: =?KOI8-R?B?4c7E0sXKIP7F0s7P1w==?= <ache@nagual.ru> To: Peter Wemm <peter@spinner.dialix.com> Cc: Mike Pritchard <mpp@freefall.freebsd.org>, Bruce Evans <bde@zeta.org.au>, cvs-all@freefall.freebsd.org, CVS-committers@freefall.freebsd.org, cvs-sys@freefall.freebsd.org Subject: Re: cvs commit: src/sys/sys types.h Message-ID: <Pine.BSF.3.95q.970216152728.392A-100000@nagual.ru> In-Reply-To: <199702160821.QAA24233@spinner.DIALix.COM>
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On Sun, 16 Feb 1997, Peter Wemm wrote:
> poll...
Well lets fix select for now and take poll as next step.
> Also, bzero(6*FD_SETSIZE...) etc can probably be fixed without too much
> pain for select() if somebody's prepared to get blood on their hands. The
> incoming bits do not appear to need to be zeroed (copyin overwrites it
> with a rounded up to byte boundary and counts the bits that it's scanning
> in selscan), and only the number of bytes that are going to be copyout'ed
> need to be zeroed.
I don't understand why rounding is even needed here (maybe to make less
overhead for p_selbits_size increasing?), but we can always
round to 256 boundary by defining FD_ROUNDSIZE=256 in sys_generic.c
> if (ni > 8) { /* 64 bits - arbitary guess at tradeoff */
> /*
> * Clear the entire return-to-user buffer space
> */
> bzero (p->p_selbits + (i + 3) * p->p_selbits_size,
^^^^^^ just 3
> p->p_selbits_size * 3);
I agree about this one too and include it the patch.
Here is the patch variant for review:
*** sys_generic.c.orig Tue Jan 14 23:11:28 1997
--- sys_generic.c Sun Feb 16 16:00:48 1997
***************
*** 508,513 ****
--- 508,515 ----
return (error);
}
+ #define FD_ROUNDSIZE 256
+
static int nselcoll;
int selwait;
***************
*** 539,545 ****
uap->nd = p->p_fd->fd_nfiles; /* forgiving; slightly wrong */
/* The amount of space we need to allocate */
! ni = howmany(roundup2 (uap->nd, FD_SETSIZE), NFDBITS) *
sizeof(fd_mask);
if (ni > p->p_selbits_size) {
--- 541,547 ----
uap->nd = p->p_fd->fd_nfiles; /* forgiving; slightly wrong */
/* The amount of space we need to allocate */
! ni = howmany(roundup2 (uap->nd, FD_ROUNDSIZE), NFDBITS) *
sizeof(fd_mask);
if (ni > p->p_selbits_size) {
***************
*** 547,553 ****
free (p->p_selbits, M_SELECT);
while (p->p_selbits_size < ni)
! p->p_selbits_size += 32; /* Increase by 256 bits */
p->p_selbits = malloc(p->p_selbits_size * 6, M_SELECT,
M_WAITOK);
--- 549,557 ----
free (p->p_selbits, M_SELECT);
while (p->p_selbits_size < ni)
! p->p_selbits_size +=
! howmany(FD_ROUNDSIZE, NFDBITS) *
! sizeof(fd_mask);
p->p_selbits = malloc(p->p_selbits_size * 6, M_SELECT,
M_WAITOK);
***************
*** 558,571 ****
p->p_selbits_size);
}
- /*
- * This buffer is usually very small therefore it's probably faster
- * to just zero it, rather than calculate what needs to be zeroed.
- */
- bzero (p->p_selbits, p->p_selbits_size * 6);
-
/* The amount of space we need to copyin/copyout */
ni = howmany(uap->nd, NFDBITS) * sizeof(fd_mask);
#define getbits(name, x) \
if (uap->name && \
--- 562,580 ----
p->p_selbits_size);
}
/* The amount of space we need to copyin/copyout */
ni = howmany(uap->nd, NFDBITS) * sizeof(fd_mask);
+
+ if (ni > 8) { /* 64 bits - arbitary guess at tradeoff */
+ /*
+ * Clear the entire return-to-user buffer space
+ */
+ bzero (p->p_selbits + 3 * p->p_selbits_size,
+ p->p_selbits_size * 3);
+ } else {
+ for (i = 0; i < 3; i++)
+ bzero(obits[i], ni);
+ }
#define getbits(name, x) \
if (uap->name && \
--
Andrey A. Chernov
<ache@null.net>
http://www.nagual.ru/~ache/
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