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* [BROKEN] mpmc_ptr_ring: Rely on null pointers to avoid p_tailjn/mpmc-nullJonathan Neuschäfer2018-06-211-38/+23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This should fix a performance problem when two (or more) producers run on the same CPU. [ TODO: more text ] previously: Thread A Thread B producer_head=1 write item <preemptive context switch> producer_head=2 write item <stalled because producer_tail is still 0> <preemptive context switch> producer_tail=1 producer_head=3 write item <stalled because producer_tail is still 1> ... with this patch: Thread A Thread B producer_head=1 write item <preemptive context switch> producer_head=2 write item producer_head=3 write item producer_head=4 write item producer_head=5 write item <preemptive context switch> producer_head=6 write item producer_head=7 write item ...
* mpmc_ptr_ring: add {,un}likely() annotationsThomas Gschwantner2018-06-211-3/+3
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* mpmc_ptr_ring: use atomic_try_cmpxchg()Thomas Gschwantner2018-06-201-12/+10
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* mpmc_ptr_ring: Fix a wordJonathan Neuschäfer2018-06-171-1/+1
| | | | Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
* mpmc_ptr_ring: Include all necessary headersJonathan Neuschäfer2018-06-121-0/+11
| | | | | | | | | | | | | | | | | | | | mpmc_ptr_ring.h should include the headers that it needs explicitly. This commit adds the following: - <asm/barrier.h>: smp_rmb, smp_wmb, smp_mb__before_atomic - <linux/atomic.h>: atomic_t, atomic_read, atomic_set, atomic_cmpxchg, atomic_inc - <linux/cache.h>: ____cacheline_aligned_in_smp - <linux/compiler.h>: READ_ONCE, WRITE_ONCE - <linux/errno.h>: ENOMEM - <linux/log2.h>: is_power_of_2 - <linux/processor.h>: cpu_relax - <linux/slab.h>: kcalloc, kfree - <linux/stddef.h>: NULL I'm not sure if all of them are really needed because I wasn't about to provoke a compile error due to the missing includes. Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
* mpmc_ptr_ring: Fix some style detailsJonathan Neuschäfer2018-06-121-1/+1
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* mpmc_ptr_ring: calculate mask once and store itThomas Gschwantner2018-06-101-3/+5
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* mpmc_ptr_ring: use unsigned int instead of size_tThomas Gschwantner2018-06-101-10/+10
| | | | | | | | For producers/consumers we use atomic_t which is really int, so size_t could either be too large, wasting memory, or too small (unlikely). For size, we also want to be using unsigned int, since the mask that we derive from it is ANDed with producer/consumer.
* mpmc_ptr_ring: add include guardThomas Gschwantner2018-06-101-0/+6
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* mpmc_ptr_ring: Switch to smp_[rw]mb()Jonathan Neuschäfer2018-06-081-8/+8
| | | | | | | | | | | | | | From https://www.kernel.org/doc/Documentation/memory-barriers.txt: > SMP memory barriers are reduced to compiler barriers on uniprocessor > compiled systems because it is assumed that a CPU will appear to be > self-consistent, and will order overlapping accesses correctly with > respect to itself. Since we only order CPU memory accesses with the memory barriers in mpmc_ptr_ring.h, smp_[rw]mb() should be sufficient. Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
* messages: Ensure that there are more queue slots than CPUsJonathan Neuschäfer2018-06-041-0/+3
| | | | | | | I'm not completely sure about this. It also doesn't fix all the errors: sometimes the test suite reports that it fails to send packets.
* mpmc_ptr_ring: Place producer_head and producer_tail in the same cachelineJonathan Neuschäfer2018-06-041-5/+3
| | | | | They are updated together, so it doesn't make much sense to keep them separate in the cache.
* mpmc_ptr_ring: Use atomic_t instead of atomic_long_tJonathan Neuschäfer2018-06-041-20/+20
| | | | The index range doesn't get large enough to warrant 64-bit indices.
* mpmc_ptr_ring: Eliminate false sharing in struct mpmc_ptr_ringJonathan Neuschäfer2018-06-041-3/+3
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* mpmc_ptr_ring: Reduce the memory barrier usageJonathan Neuschäfer2018-06-041-26/+22
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* mpmc_ptr_ring: Fix the remaining crashJonathan Neuschäfer2018-06-041-2/+2
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* [WIP] Implement a lock-free MPMC ring bufferJonathan Neuschäfer2018-06-041-0/+212
TODO: actually use the right memory barriers in the right places TODO: eliminate false sharing between mpmc_ptr_ring members TODO: reconsider atomic_long_t vs. atomic_t, vs. the type of size in _init() TODO: sprinkle likely/unlikely on some branches FIXME: it still crashes
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