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* [Qemu-devel] [PATCH v1 0/3] Fixes for TCG hangs
@ 2017-06-14 14:02 Alex Bennée
  2017-06-14 14:02 ` [Qemu-devel] [PATCH v1 1/3] vl: Fix broken thread=xxx option of the --accel parameter Alex Bennée
                   ` (4 more replies)
  0 siblings, 5 replies; 21+ messages in thread
From: Alex Bennée @ 2017-06-14 14:02 UTC (permalink / raw)
  To: peter.maydell, pbonzini, rth, cota; +Cc: qemu-devel, Alex Bennée

Hi,

This is an alternative approach to fixing the hang that Emilio zeroed
in on with:

  https://lists.nongnu.org/archive/html/qemu-devel/2017-06/msg03224.html

Instead of forcing the front-end to treat any MSRs differently we
shortcut the lookup_tb_ptr by checking for icount_decr and
cpu->interrupt_request conditions.

Fundamentally the problem was that an interrupt was pending
(interrupt_request was set) but the "msr daifclr" operations when the
kernel did local_irq/fiq_enable() never got handled because the
cpu_idle loop was being very efficiently chained. As a result we never
got around to exiting the TCG code and calling arm_cpu_do_interrupt
which would then raise the IRQ to move things on.

Emilio's fix is also correct - we should exit the loop whenever the
IRQ conditions may have changed. However by checking in the lookup_ptr
function we avoid churn in figuring out all the other cases in the
front ends. This may have a potential cost for code with lots of
calculated jumps although I would argue its fairly minimal given we've
already sucked up the cost of a helper function and I don't think the
difference between the helper function and a full exit is that
marginal.

I've also included Thomas's thread fix as it has yet to be merged.

I humbly submit my patches to the TCG gods to decide which is the best
approach ;-)

Alex Bennée (2):
  tcg-runtime: light re-factor of lookup_tb_ptr
  tcg-runtime: short-circuit lookup_tb_ptr on IRQs

Thomas Huth (1):
  vl: Fix broken thread=xxx option of the --accel parameter

 tcg-runtime.c | 52 +++++++++++++++++++++++++++++++---------------------
 vl.c          | 13 +++++--------
 2 files changed, 36 insertions(+), 29 deletions(-)

-- 
2.13.0

^ permalink raw reply	[flat|nested] 21+ messages in thread

end of thread, other threads:[~2017-06-16 20:02 UTC | newest]

Thread overview: 21+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2017-06-14 14:02 [Qemu-devel] [PATCH v1 0/3] Fixes for TCG hangs Alex Bennée
2017-06-14 14:02 ` [Qemu-devel] [PATCH v1 1/3] vl: Fix broken thread=xxx option of the --accel parameter Alex Bennée
2017-06-14 14:02 ` [Qemu-devel] [PATCH v1 2/3] tcg-runtime: light re-factor of lookup_tb_ptr Alex Bennée
2017-06-14 15:44   ` Richard Henderson
2017-06-14 16:07     ` Alex Bennée
2017-06-14 17:10   ` Pranith Kumar
2017-06-14 14:02 ` [Qemu-devel] [PATCH v1 3/3] tcg-runtime: short-circuit lookup_tb_ptr on IRQs Alex Bennée
2017-06-14 15:45   ` Richard Henderson
2017-06-14 16:08     ` Paolo Bonzini
2017-06-14 16:51       ` Richard Henderson
2017-06-14 17:08         ` Paolo Bonzini
2017-06-14 18:26           ` Richard Henderson
2017-06-14 19:07             ` Alex Bennée
2017-06-14 19:43               ` Richard Henderson
2017-06-16 20:01                 ` Emilio G. Cota
2017-06-14 17:49       ` Alex Bennée
2017-06-14 17:53         ` Richard Henderson
2017-06-14 19:11         ` Peter Maydell
2017-06-14 19:19           ` Richard Henderson
2017-06-14 14:25 ` [Qemu-devel] [PATCH v1 0/3] Fixes for TCG hangs Philippe Mathieu-Daudé
2017-06-14 14:30 ` no-reply

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