From: "David S. Miller" <davem@caip.rutgers.edu>
To: tridge@cs.anu.edu.au
Cc: lmlinux@neteng.engr.sgi.com, torvalds@cs.helsinki.fi
Subject: wicked checksum optimization...
Date: Mon, 13 May 1996 00:05:04 -0400 [thread overview]
Message-ID: <199605130405.AAA05898@huahaga.rutgers.edu> (raw)
I think I figured out how to do it all "the right way(tm)"
The big problem is alignment, but %97 of the time the buffer is
aligned how we like. I've decided it is ok to take the hit of an
unaligned access trap for the %3 cases, but not that much of a hit.
The implementation looks like this:
All loads and stores in the ip checksum routines will look the same,
the only time we do stores is for the csum/copy routines. Anyways the
eight instruction codes recognized will be for:
ld [%o0 + offset], %o4
ld [%o0 + offset], %o5
lduh [%o0 + offset], %o4
lduh [%o0 + offset], %o5
st %o4, [%g3 + offset]
st %o5, [%g3 + offset]
sth %o4, [%g3 + offset]
sth %o5, [%g3 + offset]
The unaligned trap handler (before it even tries to save any state)
will look something like:
mna_trap:
andcc %l0, PSR_PS, %g0
be,a mna_fromuser
ld [%l1], %l5
sethi %hi(LOAD_O4), %l4
and %l5, %l4, %l6
cmp %l6, %l4
bne 1f
sethi %hi(LOAD_O5), %l4
mov %l1, %g6 ! %pc
sethi %hi(C_LABEL(csum_ldo4_fixup)), %l1
or %l1, %lo(C_LABEL(csum_ldo4_fixup)), %l1
wr %l0, 0x0, %psr ! fix cond-codes
and %l5, LOAD_IMMEDIATE_FIELD, %g7
srl %g7, LOAD_IMMEDIATE_SHIFT, %g7 ! offset
jmp %l1
rett %l1 + 0x4
1:
/* etc. for other instructions recognized */
mna_fromuser:
SAVE_ALL
/* From user mode or something we don't handle for the
* kernel.
*/
call C_LABEL(do_mna)
nop
RESTORE_ALL
Ok, now the fixup routines just look like:
csum_ldo4_fixup:
ldub [%o0 + %g7], %g4
add %g7, 1, %g7
ldub [%o0 + %g7], %g5
sll %g4, 24, %g4
add %g7, 1, %g7
sll %g5, 16, %g5
or %g4, %g5, %o4
ldub [%o0 + %g7], %g4
add %g7, 1, %g7
ldub [%o0 + %g7], %g5
sll %g4, 8, %g4
or %g5, %g4, %g4
jmp %g6 ! wheee...
or %o4, %g4, %o4
and so on... then csum_parial and friends can just blaze through
assuming proper alignment for all pointers to the packet contents
etc. Nifty eh? Sparc is fun...
Later,
David S. Miller
davem@caip.rutgers.edu
reply other threads:[~1996-05-13 14:28 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=199605130405.AAA05898@huahaga.rutgers.edu \
--to=davem@caip.rutgers.edu \
--cc=lmlinux@neteng.engr.sgi.com \
--cc=torvalds@cs.helsinki.fi \
--cc=tridge@cs.anu.edu.au \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.