diff options
| author |   Heiko Carstens <hca@linux.ibm.com> | 2020-12-04 12:32:42 +0100 |
|---|---|---|
| committer | Heiko Carstens <hca@linux.ibm.com> | 2020-12-16 14:55:49 +0100 |
| commit | dd6cfe553212b6311cac27ecd2f67621857fb10a (patch) | |
| tree | 75a5501adcd811dd9647cd7835d98fafdee32b8c /arch/s390/kernel/entry.S | |
| parent | s390/test_unwind: use timer instead of udelay (diff) | |
| download | linux-dev-dd6cfe553212b6311cac27ecd2f67621857fb10a.tar.xz linux-dev-dd6cfe553212b6311cac27ecd2f67621857fb10a.zip | |
s390/delay: simplify udelay
udelay is implemented by using quite subtle details to make it
possible to load an idle psw and waiting for an interrupt even in irq
context or when interrupts are disabled. Also handling (or better: no
handling) of softirqs is taken into account.
All this is done to optimize for something which should in normal
circumstances never happen: calling udelay to busy wait. Therefore get
rid of the whole complexity and just busy loop like other
architectures are doing it also.
It could have been possible to use diag 0x44 instead of cpu_relax() in
the busy loop, however we have seen too many bad things happen with
diag 0x44 that it seems to be better to simply busy loop.
Also note that with this new implementation kernel preemption does
work when within the udelay loop. This did not work before.
To get a feeling what the former code optimizes for: IPL'ing a kernel
with 'defconfig' and afterwards compiling a kernel ends with a total
of zero udelay calls.
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'arch/s390/kernel/entry.S')
| -rw-r--r-- | arch/s390/kernel/entry.S | 4 |
1 files changed, 0 insertions, 4 deletions
diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S index 2cc338aa3f65..87e83164c330 100644 --- a/arch/s390/kernel/entry.S +++ b/arch/s390/kernel/entry.S @@ -779,8 +779,6 @@ ENTRY(io_int_handler) xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) TRACE_IRQS_OFF - TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ - jo .Lio_restore .Lio_loop: lgr %r2,%r11 # pass pointer to pt_regs lghi %r3,IO_INTERRUPT @@ -967,8 +965,6 @@ ENTRY(ext_int_handler) xc __PT_FLAGS(8,%r11),__PT_FLAGS(%r11) xc __SF_BACKCHAIN(8,%r15),__SF_BACKCHAIN(%r15) TRACE_IRQS_OFF - TSTMSK __LC_CPU_FLAGS,_CIF_IGNORE_IRQ - jo .Lio_restore lgr %r2,%r11 # pass pointer to pt_regs lghi %r3,EXT_INTERRUPT brasl %r14,do_IRQ |