* [PATCH 00/14] entry: preempt_schedule_irq() callers scrub
@ 2019-03-11 22:47 Valentin Schneider
2019-03-11 22:47 ` [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop Valentin Schneider
2019-03-12 18:03 ` [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Vineet Gupta
0 siblings, 2 replies; 5+ messages in thread
From: Valentin Schneider @ 2019-03-11 22:47 UTC (permalink / raw)
To: linux-kernel
Cc: uclinux-h8-devel, linux-xtensa, linux-ia64, linux-c6x-dev,
Julien Thierry, Peter Zijlstra, linux-s390, x86, linux-mips,
linux-m68k, Ingo Molnar, linux-sh, sparclinux, nios2-dev,
Thomas Gleixner, linux-snps-arc, linuxppc-dev, linux-riscv
Hi,
This is the continuation of [1] where I'm hunting down
preempt_schedule_irq() callers because of [2].
I told myself the best way to get this moving forward wouldn't be to write
doc about it, but to go write some fixes and get some discussions going,
which is what this patch-set is about.
I've looked at users of preempt_schedule_irq(), and made sure they didn't
have one of those useless loops. The list of offenders is:
$ grep -r -I "preempt_schedule_irq" arch/ | cut -d/ -f2 | sort | uniq
arc
arm
arm64
c6x
csky
h8300
ia64
m68k
microblaze
mips
nds32
nios2
parisc
powerpc
riscv
s390
sh
sparc
x86
xtensa
Regarding that loop, archs seem to fall in 3 categories:
A) Those that don't have the loop
B) Those that have a small need_resched() loop around the
preempt_schedule_irq() callsite
C) Those that branch to some more generic code further up the entry code
and eventually branch back to preempt_schedule_irq()
arc, m68k, nios2 fall in A)
sparc, ia64, s390 fall in C)
all the others fall in B)
I've written patches for B) and C) EXCEPT for ia64 and s390 because I
haven't been able to tell if it's actually fine to kill that "long jump"
(and maybe I'm wrong on sparc). Hopefully folks who understand what goes on
in there might be able to shed some light.
Also, since I sent patches for arm & arm64 in [1] I'm not including them
here.
Boot-tested on:
- x86
Build-tested on:
- h8300
- c6x
- powerpc
- mips
- nds32
- microblaze
- sparc
- xtensa
Thanks,
Valentin
[1]: https://lore.kernel.org/lkml/20190131182339.9835-1-valentin.schneider@arm.com/
[2]: https://lore.kernel.org/lkml/cc989920-a13b-d53b-db83-1584a7f53edc@arm.com/
Valentin Schneider (14):
sched/core: Fix preempt_schedule() interrupt return comment
c6x: entry: Remove unneeded need_resched() loop
csky: entry: Remove unneeded need_resched() loop
h8300: entry: Remove unneeded need_resched() loop
microblaze: entry: Remove unneeded need_resched() loop
MIPS: entry: Remove unneeded need_resched() loop
nds32: ex-exit: Remove unneeded need_resched() loop
powerpc: entry: Remove unneeded need_resched() loop
RISC-V: entry: Remove unneeded need_resched() loop
sh: entry: Remove unneeded need_resched() loop
sh64: entry: Remove unneeded need_resched() loop
sparc64: rtrap: Remove unneeded need_resched() loop
x86/entry: Remove unneeded need_resched() loop
xtensa: entry: Remove unneeded need_resched() loop
arch/c6x/kernel/entry.S | 3 +--
arch/csky/kernel/entry.S | 4 ----
arch/h8300/kernel/entry.S | 3 +--
arch/microblaze/kernel/entry.S | 5 -----
arch/mips/kernel/entry.S | 3 +--
arch/nds32/kernel/ex-exit.S | 4 ++--
arch/powerpc/kernel/entry_32.S | 6 +-----
arch/powerpc/kernel/entry_64.S | 8 +-------
arch/riscv/kernel/entry.S | 3 +--
arch/sh/kernel/cpu/sh5/entry.S | 5 +----
arch/sh/kernel/entry-common.S | 4 +---
arch/sparc/kernel/rtrap_64.S | 1 -
arch/x86/entry/entry_32.S | 3 +--
arch/x86/entry/entry_64.S | 3 +--
arch/xtensa/kernel/entry.S | 2 +-
kernel/sched/core.c | 7 +++----
16 files changed, 16 insertions(+), 48 deletions(-)
--
2.20.1
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop
2019-03-11 22:47 [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Valentin Schneider
@ 2019-03-11 22:47 ` Valentin Schneider
2019-05-03 6:59 ` Michael Ellerman
2019-03-12 18:03 ` [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Vineet Gupta
1 sibling, 1 reply; 5+ messages in thread
From: Valentin Schneider @ 2019-03-11 22:47 UTC (permalink / raw)
To: linux-kernel; +Cc: Paul Mackerras, linuxppc-dev
Since the enabling and disabling of IRQs within preempt_schedule_irq()
is contained in a need_resched() loop, we don't need the outer arch
code loop.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
---
arch/powerpc/kernel/entry_32.S | 6 +-----
arch/powerpc/kernel/entry_64.S | 8 +-------
2 files changed, 2 insertions(+), 12 deletions(-)
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 0768dfd8a64e..ff3fe3824a4a 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -896,11 +896,7 @@ resume_kernel:
*/
bl trace_hardirqs_off
#endif
-1: bl preempt_schedule_irq
- CURRENT_THREAD_INFO(r9, r1)
- lwz r3,TI_FLAGS(r9)
- andi. r0,r3,_TIF_NEED_RESCHED
- bne- 1b
+ bl preempt_schedule_irq
#ifdef CONFIG_TRACE_IRQFLAGS
/* And now, to properly rebalance the above, we tell lockdep they
* are being turned back on, which will happen when we return
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 435927f549c4..9c86c6826856 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -857,13 +857,7 @@ resume_kernel:
* sure we are soft-disabled first and reconcile irq state.
*/
RECONCILE_IRQ_STATE(r3,r4)
-1: bl preempt_schedule_irq
-
- /* Re-test flags and eventually loop */
- CURRENT_THREAD_INFO(r9, r1)
- ld r4,TI_FLAGS(r9)
- andi. r0,r4,_TIF_NEED_RESCHED
- bne 1b
+ bl preempt_schedule_irq
/*
* arch_local_irq_restore() from preempt_schedule_irq above may
--
2.20.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH 00/14] entry: preempt_schedule_irq() callers scrub
2019-03-11 22:47 [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Valentin Schneider
2019-03-11 22:47 ` [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop Valentin Schneider
@ 2019-03-12 18:03 ` Vineet Gupta
2019-03-12 18:18 ` Valentin Schneider
1 sibling, 1 reply; 5+ messages in thread
From: Vineet Gupta @ 2019-03-12 18:03 UTC (permalink / raw)
To: Valentin Schneider, linux-kernel
Cc: uclinux-h8-devel, linux-xtensa, linux-ia64, linux-c6x-dev,
Julien Thierry, Peter Zijlstra, linux-s390, x86, linux-mips,
linux-m68k, Ingo Molnar, linux-sh, sparclinux, nios2-dev,
Thomas Gleixner, linux-snps-arc, linuxppc-dev, linux-riscv
On 3/11/19 3:47 PM, Valentin Schneider wrote:
> Hi,
>
> This is the continuation of [1] where I'm hunting down
> preempt_schedule_irq() callers because of [2].
>
> I told myself the best way to get this moving forward wouldn't be to write
> doc about it, but to go write some fixes and get some discussions going,
> which is what this patch-set is about.
>
> I've looked at users of preempt_schedule_irq(), and made sure they didn't
> have one of those useless loops. The list of offenders is:
>
> $ grep -r -I "preempt_schedule_irq" arch/ | cut -d/ -f2 | sort | uniq
>
...
>
> Regarding that loop, archs seem to fall in 3 categories:
> A) Those that don't have the loop
Please clarify that this is the right thing to do (since core code already has the
loop) hence no fixing is required for this "category"
> B) Those that have a small need_resched() loop around the
> preempt_schedule_irq() callsite
> C) Those that branch to some more generic code further up the entry code
> and eventually branch back to preempt_schedule_irq()
>
> arc, m68k, nios2 fall in A)
> sparc, ia64, s390 fall in C)
> all the others fall in B)
>
> I've written patches for B) and C) EXCEPT for ia64 and s390 because I
> haven't been able to tell if it's actually fine to kill that "long jump"
> (and maybe I'm wrong on sparc). Hopefully folks who understand what goes on
> in there might be able to shed some light.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 00/14] entry: preempt_schedule_irq() callers scrub
2019-03-12 18:03 ` [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Vineet Gupta
@ 2019-03-12 18:18 ` Valentin Schneider
0 siblings, 0 replies; 5+ messages in thread
From: Valentin Schneider @ 2019-03-12 18:18 UTC (permalink / raw)
To: Vineet Gupta, linux-kernel
Cc: uclinux-h8-devel, linux-xtensa, linux-ia64, linux-c6x-dev,
Julien Thierry, Peter Zijlstra, linux-s390, x86, linux-mips,
linux-m68k, Ingo Molnar, linux-sh, sparclinux, nios2-dev,
Thomas Gleixner, linux-snps-arc, linuxppc-dev, linux-riscv
On 12/03/2019 18:03, Vineet Gupta wrote:
[...]
>> Regarding that loop, archs seem to fall in 3 categories:
>> A) Those that don't have the loop
>
> Please clarify that this is the right thing to do (since core code already has the
> loop) hence no fixing is required for this "category"
>
Right, those don't need any change. I had a brief look at them to double
check they had the proper need_resched() gate before calling
preempt_schedule_irq() (with no loop) and they all seem fine. Also...
>> B) Those that have a small need_resched() loop around the
>> preempt_schedule_irq() callsite
>> C) Those that branch to some more generic code further up the entry code
>> and eventually branch back to preempt_schedule_irq()
>>
>> arc, m68k, nios2 fall in A)
>
I forgot to include parisc in here.
[...]
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop
2019-03-11 22:47 ` [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop Valentin Schneider
@ 2019-05-03 6:59 ` Michael Ellerman
0 siblings, 0 replies; 5+ messages in thread
From: Michael Ellerman @ 2019-05-03 6:59 UTC (permalink / raw)
To: Valentin Schneider, linux-kernel; +Cc: linuxppc-dev, Paul Mackerras
On Mon, 2019-03-11 at 22:47:46 UTC, Valentin Schneider wrote:
> Since the enabling and disabling of IRQs within preempt_schedule_irq()
> is contained in a need_resched() loop, we don't need the outer arch
> code loop.
>
> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: linuxppc-dev@lists.ozlabs.org
Applied to powerpc next, thanks.
https://git.kernel.org/powerpc/c/90437bffa5f9b1440ba03e023f4875d1
cheers
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-05-03 7:11 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-03-11 22:47 [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Valentin Schneider
2019-03-11 22:47 ` [PATCH 08/14] powerpc: entry: Remove unneeded need_resched() loop Valentin Schneider
2019-05-03 6:59 ` Michael Ellerman
2019-03-12 18:03 ` [PATCH 00/14] entry: preempt_schedule_irq() callers scrub Vineet Gupta
2019-03-12 18:18 ` Valentin Schneider
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).