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Having two ring buffers per-peer means that every peer results in two
massive ring allocations. On an 8-core x86_64 machine, this commit
reduces the per-peer allocation from 18,688 bytes to 1,856 bytes, which
is an 90% reduction. Ninety percent! With some single-machine
deployments approaching 500,000 peers, we're talking about a reduction
from 7 gigs of memory down to 700 megs of memory.
In order to get rid of these per-peer allocations, this commit switches
to using a list-based queueing approach. Currently GSO fragments are
chained together using the skb->next pointer (the skb_list_* singly
linked list approach), so we form the per-peer queue around the unused
skb->prev pointer (which sort of makes sense because the links are
pointing backwards). Use of skb_queue_* is not possible here, because
that is based on doubly linked lists and spinlocks. Multiple cores can
write into the queue at any given time, because its writes occur in the
start_xmit path or in the udp_recv path. But reads happen in a single
workqueue item per-peer, amounting to a multi-producer, single-consumer
paradigm.
The MPSC queue is implemented locklessly and never blocks. However, it
is not linearizable (though it is serializable), with a very tight and
unlikely race on writes, which, when hit (some tiny fraction of the
0.15% of partial adds on a fully loaded 16-core x86_64 system), causes
the queue reader to terminate early. However, because every packet sent
queues up the same workqueue item after it is fully added, the worker
resumes again, and stopping early isn't actually a problem, since at
that point the packet wouldn't have yet been added to the encryption
queue. These properties allow us to avoid disabling interrupts or
spinning. The design is based on Dmitry Vyukov's algorithm [1].
Performance-wise, ordinarily list-based queues aren't preferable to
ringbuffers, because of cache misses when following pointers around.
However, we *already* have to follow the adjacent pointers when working
through fragments, so there shouldn't actually be any change there. A
potential downside is that dequeueing is a bit more complicated, but the
ptr_ring structure used prior had a spinlock when dequeueing, so all and
all the difference appears to be a wash.
Actually, from profiling, the biggest performance hit, by far, of this
commit winds up being atomic_add_unless(count, 1, max) and atomic_
dec(count), which account for the majority of CPU time, according to
perf. In that sense, the previous ring buffer was superior in that it
could check if it was full by head==tail, which the list-based approach
cannot do.
But all and all, this enables us to get massive memory savings, allowing
WireGuard to scale for real world deployments, without taking much of a
performance hit.
[1] http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Prior, if the alloc_percpu of packet_percpu_multicore_worker_alloc
failed, the previously allocated ptr_ring wouldn't be freed. This commit
adds the missing call to ptr_ring_cleanup in the error case.
Reported-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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I understand why this must be done, though I'm not so happy about having
to do it. In some places, it puts us over 80 chars and we have to break
lines up in further ugly ways. And in general, I think this makes things
harder to read. Yet another thing we must do to please upstream.
Maybe this can be replaced in the future by some kind of automatic
module namespacing logic in the linker, or even combined with LTO and
aggressive symbol stripping.
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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The kernel has very specific rules correlating file type with comment
type, and also SPDX identifiers can't be merged with other comments.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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This is the worst commit in the whole repo, making the code much less
readable, but so it goes with upstream maintainers.
We are now woefully wrapped at 80 columns.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Suggested-by: Jason A. Donenfeld <Jason@zx2c4.com>
[Jason: fixed up the flushing of the rx_queue in peer_remove]
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Since these are the only consumers, there's no need for locking.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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It's good to have SPDX identifiers in all files as the Linux kernel
developers are working to add these identifiers to all files.
Update all files with the correct SPDX license identifier based on the license
text of the project or based on the license in the file itself. The SPDX
identifier is a legally binding shorthand, which can be used instead of the
full boiler plate text.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Modified-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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One types:
for (i = 0 ...
So one should also type:
for_each_obj (obj ...
But the upstream kernel style guidelines are insane, and so we must
instead do:
for_each_obj(obj ...
Ugly, but one must choose his battles wisely.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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This removes our dependency on padata and moves to a different mode of
multiprocessing that is more efficient.
This began as Samuel Holland's GSoC project and was gradually
reworked/redesigned/rebased into this present commit, which is a
combination of his initial contribution and my subsequent rewriting and
redesigning.
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
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