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lkl: Direct irq and fix direct syscall degration #257

Merged
merged 2 commits into from
Nov 3, 2016
Merged

lkl: Direct irq and fix direct syscall degration #257

merged 2 commits into from
Nov 3, 2016

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liuyuan10
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@liuyuan10 liuyuan10 commented Nov 2, 2016 •
edited by thehajime
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There is two major issues in current direct syscall implementation:

  1. When there is already a thread pending in syscall, direct syscall
    degrages to wakeup idle and the performance is bad in that case. This is
    actually common in applications that have a trafficless control
    connection.
  2. IRQ is not direct if LKL is in idle.

Both issuses are actually because of the same thing: LKL can't
reschedule when LKL is in idle. The patch adds such support.

There are two downside of this patch:

  1. need to change kernel/sched/idle.c to expose cpu_idle_loop.
  2. lkl_idle_tail_schedule must be in sync with idle.c

There downsides seem OK given the performance we achieve from this
patch.

For common case, it saves one context switch (direct irq) and I can
observe 10% TCP_RR improvement on my desktop.

This change is Reviewable

@liuyuan10
lkl: expose cpu_idle_loop from idle.c
9072b9a 
Direct irq needs this function to handle idle loop by itself

Signed-off-by: Yuan Liu <liuyuan@google.com>
tavip
tavip reviewed Nov 2, 2016
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Looks good to me. I think we can remove the test_atomic_... function and use test_bit, see the inline comments.

arch/lkl/kernel/threads.c
return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}


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test_bit is already non-atomic in our case, see asm-generic/bitops/atomic.h

@thehajime thehajime mentioned this pull request Nov 2, 2016
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Thanks for the quick review. I was thinking to avoid future change of test_bit breaking LKL but it's fine to me to keep it clean. Removed the test_bit...

@liuyuan10
lkl: Direct irq and fix direct syscall degration
3b62e66 
There are two major issues in current direct syscall implementation:

1. When there is already a thread pending in syscall, direct syscall
degrages to wakeup idle and the performance is bad in that case. This is
actually common in applications that have a trafficless control
connection.
2. IRQ is not direct if LKL is in idle.

Both issuses are actually because of the same thing: LKL can't
reschedule when LKL is in idle. The patch adds such support.

There are two downside of this patch:
1. need to change kernel/sched/idle.c to expose cpu_idle_loop.
2. lkl_idle_tail_schedule must be in sync with idle.c

Those downsides seem OK given the performance we achieve from this
patch.

For common case, it saves one context switch (direct irq) and I can
observe 10% TCP_RR improvement on my desktop.

Signed-off-by: Yuan Liu <liuyuan@google.com>
@tavip tavip merged commit 468cb6e into lkl:master Nov 3, 2016
@liuyuan10 liuyuan10 deleted the dirq branch November 3, 2016 18:09
@laijs
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laijs commented Feb 13, 2017

hello @liuyuan10
what does 2. IRQ is not direct if LKL is in idle. mean?

before this patch, the idle thread had enable irqs now to allow direct irqs to run before lkl_ops->sem_down(cpu.idle_sem)

rodionov pushed a commit to rodionov/lkl that referenced this pull request Jan 2, 2025
@borkmann
selftests/bpf: Test bpf_mprog query API via libbpf and raw syscall
f9b0879 
Add a new test case which performs double query of the bpf_mprog through
libbpf API, but also via raw bpf(2) syscall. This is testing to gather
first the count and then in a subsequent probe the full information with
the program array without clearing passed structs in between.

  # ./vmtest.sh -- ./test_progs -t tc_opts
  [...]
  ./test_progs -t tc_opts
  [    1.398818] tsc: Refined TSC clocksource calibration: 3407.999 MHz
  [    1.400263] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x311fd336761, max_idle_ns: 440795243819 ns
  [    1.402734] clocksource: Switched to clocksource tsc
  [    1.426639] bpf_testmod: loading out-of-tree module taints kernel.
  [    1.428112] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
  lkl#252     tc_opts_after:OK
  lkl#253     tc_opts_append:OK
  lkl#254     tc_opts_basic:OK
  lkl#255     tc_opts_before:OK
  lkl#256     tc_opts_chain_classic:OK
  lkl#257     tc_opts_chain_mixed:OK
  lkl#258     tc_opts_delete_empty:OK
  lkl#259     tc_opts_demixed:OK
  lkl#260     tc_opts_detach:OK
  lkl#261     tc_opts_detach_after:OK
  lkl#262     tc_opts_detach_before:OK
  lkl#263     tc_opts_dev_cleanup:OK
  lkl#264     tc_opts_invalid:OK
  lkl#265     tc_opts_max:OK
  lkl#266     tc_opts_mixed:OK
  lkl#267     tc_opts_prepend:OK
  lkl#268     tc_opts_query:OK            <--- (new test)
  lkl#269     tc_opts_replace:OK
  lkl#270     tc_opts_revision:OK
  Summary: 19/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20231006220655.1653-4-daniel@iogearbox.net
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
rodionov pushed a commit to rodionov/lkl that referenced this pull request Jan 2, 2025
@borkmann
selftests/bpf: Test query on empty mprog and pass revision into attach
685446b 
Add a new test case to query on an empty bpf_mprog and pass the revision
directly into expected_revision for attachment to assert that this does
succeed.

  ./test_progs -t tc_opts
  [    1.406778] tsc: Refined TSC clocksource calibration: 3407.990 MHz
  [    1.408863] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x311fcaf6eb0, max_idle_ns: 440795321766 ns
  [    1.412419] clocksource: Switched to clocksource tsc
  [    1.428671] bpf_testmod: loading out-of-tree module taints kernel.
  [    1.430260] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
  lkl#252     tc_opts_after:OK
  lkl#253     tc_opts_append:OK
  lkl#254     tc_opts_basic:OK
  lkl#255     tc_opts_before:OK
  lkl#256     tc_opts_chain_classic:OK
  lkl#257     tc_opts_chain_mixed:OK
  lkl#258     tc_opts_delete_empty:OK
  lkl#259     tc_opts_demixed:OK
  lkl#260     tc_opts_detach:OK
  lkl#261     tc_opts_detach_after:OK
  lkl#262     tc_opts_detach_before:OK
  lkl#263     tc_opts_dev_cleanup:OK
  lkl#264     tc_opts_invalid:OK
  lkl#265     tc_opts_max:OK
  lkl#266     tc_opts_mixed:OK
  lkl#267     tc_opts_prepend:OK
  lkl#268     tc_opts_query:OK
  lkl#269     tc_opts_query_attach:OK     <--- (new test)
  lkl#270     tc_opts_replace:OK
  lkl#271     tc_opts_revision:OK
  Summary: 20/0 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20231006220655.1653-6-daniel@iogearbox.net
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
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@liuyuan10 @laijs @tavip