d/freebsd-dev
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Revert one chunk from commit 285362, which introduced an off-by-one error

Browse Source 
in computing a shift index. The error was due to the use of mixed
fls() / __fls() functions in another implementation of qfq.
To avoid that the problem occurs again, properly document which
incarnation of the function we need.
Note that the bug only affects QFQ in FreeBSD head from last july, as
the patch was not merged to other versions.
This commit is contained in:
Luigi Rizzo 2016-01-26 04:48:24 +00:00
parent 49d36ba409
commit f51b072d4c
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=294761
1 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
sys/netpfil/ipfw/dn_sched_qfq.c
View File

@ -60,6 +60,10 @@ typedef unsigned long bitmap;
/*
* bitmaps ops are critical. Some linux versions have __fls
* and the bitmap ops. Some machines have ffs
* NOTE: fls() returns 1 for the least significant bit,
* __fls() returns 0 for the same case.
* We use the base-0 version __fls() to match the description in
* the ToN QFQ paper
*/
#if defined(_WIN32) || (defined(__MIPSEL__) && defined(LINUX_24))
int fls(unsigned int n)
@ -409,8 +413,8 @@ qfq_make_eligible(struct qfq_sched *q, uint64_t old_V)
old_vslot = old_V >> QFQ_MIN_SLOT_SHIFT;
if (vslot != old_vslot) {
/* should be 1ULL not 2ULL */
mask = (1ULL << (__fls(vslot ^ old_vslot))) - 1;
/* must be 2ULL, see ToN QFQ article fig.5, we use base-0 fls */
mask = (2ULL << (__fls(vslot ^ old_vslot))) - 1;
qfq_move_groups(q, mask, IR, ER);
qfq_move_groups(q, mask, IB, EB);
}