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author | Ahmed S. Darwish <a.darwish@linutronix.de> | 2021-10-16 10:49:07 +0200 |
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committer | David S. Miller <davem@davemloft.net> | 2021-10-18 13:54:41 +0200 |
commit | 67c9e6270f3013e4d86ec57c4e7f27459f2a0652 (patch) | |
tree | 69cab1b15c62cd3dd449820ceebdd18107114c68 /net/batman-adv | |
parent | u64_stats: Introduce u64_stats_set() (diff) | |
download | linux-67c9e6270f3013e4d86ec57c4e7f27459f2a0652.tar.xz linux-67c9e6270f3013e4d86ec57c4e7f27459f2a0652.zip |
net: sched: Protect Qdisc::bstats with u64_stats
The not-per-CPU variant of qdisc tc (traffic control) statistics,
Qdisc::gnet_stats_basic_packed bstats, is protected with Qdisc::running
sequence counter.
This sequence counter is used for reliably protecting bstats reads from
parallel writes. Meanwhile, the seqcount's write section covers a much
wider area than bstats update: qdisc_run_begin() => qdisc_run_end().
That read/write section asymmetry can lead to needless retries of the
read section. To prepare for removing the Qdisc::running sequence
counter altogether, introduce a u64_stats sync point inside bstats
instead.
Modify _bstats_update() to start/end the bstats u64_stats write
section.
For bisectability, and finer commits granularity, the bstats read
section is still protected with a Qdisc::running read/retry loop and
qdisc_run_begin/end() still starts/ends that seqcount write section.
Once all call sites are modified to use _bstats_update(), the
Qdisc::running seqcount will be removed and bstats read/retry loop will
be modified to utilize the internal u64_stats sync point.
Note, using u64_stats implies no sequence counter protection for 64-bit
architectures. This can lead to the statistics "packets" vs. "bytes"
values getting out of sync on rare occasions. The individual values will
still be valid.
[bigeasy: Minor commit message edits, init all gnet_stats_basic_packed.]
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/batman-adv')
0 files changed, 0 insertions, 0 deletions