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author | Marcelo Tosatti <mtosatti@redhat.com> | 2023-06-27 17:08:15 -0300 |
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committer | Christian Brauner <brauner@kernel.org> | 2023-08-15 08:32:44 +0200 |
commit | 8a237adf213d73671992266eff7437f1b9f40567 (patch) | |
tree | 8ee8469ad197f0fdc7108e5de0311f41bc29a0e3 /Documentation | |
parent | d80a8f1b58c2bc8d7c6bfb65401ea4f7ec8cddc2 (diff) | |
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fs/buffer.c: disable per-CPU buffer_head cache for isolated CPUs
For certain types of applications (for example PLC software or
RAN processing), upon occurrence of an event, it is necessary to
complete a certain task in a maximum amount of time (deadline).
One way to express this requirement is with a pair of numbers,
deadline time and execution time, where:
* deadline time: length of time between event and deadline.
* execution time: length of time it takes for processing of event
to occur on a particular hardware platform
(uninterrupted).
The particular values depend on use-case. For the case
where the realtime application executes in a virtualized
guest, an IPI which must be serviced in the host will cause
the following sequence of events:
1) VM-exit
2) execution of IPI (and function call)
3) VM-entry
Which causes an excess of 50us latency as observed by cyclictest
(this violates the latency requirement of vRAN application with 1ms TTI,
for example).
invalidate_bh_lrus calls an IPI on each CPU that has non empty
per-CPU cache:
on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1);
The performance when using the per-CPU LRU cache is as follows:
42 ns per __find_get_block
68 ns per __find_get_block_slow
Given that the main use cases for latency sensitive applications
do not involve block I/O (data necessary for program operation is
locked in RAM), disable per-CPU buffer_head caches for isolated CPUs.
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Message-Id: <ZJtBrybavtb1x45V@tpad>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'Documentation')
0 files changed, 0 insertions, 0 deletions