Re: ARM softirqs

Andrea Arcangeli (andrea@suse.de)
Mon, 3 Sep 2001 17:12:58 +0200

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On Thu, Aug 30, 2001 at 12:32:39AM +0200, Andrea Arcangeli wrote:
> On Wed, Aug 29, 2001 at 05:25:34PM +0200, Andrea Arcangeli wrote:
> How does this look? (untested, I will test it later together with a
> dozen of other changes)
>
> btw, a number of other archs was buggy the same way as arm or it will
> benefit by this change the same way as arm.
>
> I will send to Linus after it is tested.

Linus please include this patch in next kernel. In short Russell pointed
out that the risc port aren't handy in implementing a very lightweight
set bit atomic with respect to interrupts (so only atomic with respect
to the local cpu) because they are missing an "or" or "bit set"
instruction between a register and memory.

Having __cpu_raise_softirq atomic against interrupts only allows us to
re-enable irqs a few cycles before, so it's only a micro irq latency
optimization, it doesn't save cpu cycles so it doesn't worth to hurt
the risc chips for it.

Now both cpu_raise_softirq and __cpu_raise_softirq must be recalled with
irq disabled, only raise_softirq can be called in whatever irq state.

diff -urN 2.4.10pre2aa1/include/asm-alpha/softirq.h 2.4.10pre2aa1-softirq/include/asm-alpha/softirq.h
--- 2.4.10pre2aa1/include/asm-alpha/softirq.h Sat Jul 21 00:04:29 2001
+++ 2.4.10pre2aa1-softirq/include/asm-alpha/softirq.h Thu Aug 30 00:22:58 2001
@@ -32,6 +32,4 @@

#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

-#define __cpu_raise_softirq(cpu, nr) set_bit(nr, &softirq_pending(cpu))
-
#endif /* _ALPHA_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-arm/softirq.h 2.4.10pre2aa1-softirq/include/asm-arm/softirq.h
--- 2.4.10pre2aa1/include/asm-arm/softirq.h Thu Aug 16 22:03:39 2001
+++ 2.4.10pre2aa1-softirq/include/asm-arm/softirq.h Thu Aug 30 00:23:00 2001
@@ -21,6 +21,4 @@
__asm__("bl%? __do_softirq": : : "lr");/* out of line */\
} while (0)

-#define __cpu_raise_softirq(cpu, nr) __set_bit(nr, &softirq_pending(cpu))
-
#endif /* __ASM_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-cris/softirq.h 2.4.10pre2aa1-softirq/include/asm-cris/softirq.h
--- 2.4.10pre2aa1/include/asm-cris/softirq.h Sat Aug 11 08:04:23 2001
+++ 2.4.10pre2aa1-softirq/include/asm-cris/softirq.h Thu Aug 30 00:23:03 2001
@@ -27,6 +27,4 @@

#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

-#define __cpu_raise_softirq(cpu,nr) set_bit((nr), &softirq_pending(cpu))
-
#endif /* __ASM_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-i386/softirq.h 2.4.10pre2aa1-softirq/include/asm-i386/softirq.h
--- 2.4.10pre2aa1/include/asm-i386/softirq.h Wed Aug 29 15:05:25 2001
+++ 2.4.10pre2aa1-softirq/include/asm-i386/softirq.h Thu Aug 30 00:22:53 2001
@@ -45,6 +45,4 @@
/* no registers clobbered */ ); \
} while (0)

-#define __cpu_raise_softirq(cpu, nr) __set_bit(nr, &softirq_pending(cpu))
-
#endif /* __ASM_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-ia64/softirq.h 2.4.10pre2aa1-softirq/include/asm-ia64/softirq.h
--- 2.4.10pre2aa1/include/asm-ia64/softirq.h Sat Aug 11 08:04:25 2001
+++ 2.4.10pre2aa1-softirq/include/asm-ia64/softirq.h Thu Aug 30 00:23:06 2001
@@ -18,8 +18,6 @@
} while (0)

-#define __cpu_raise_softirq(cpu,nr) set_bit((nr), &softirq_pending(cpu))
-
#define in_softirq() (local_bh_count() != 0)

#endif /* _ASM_IA64_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-ppc/softirq.h 2.4.10pre2aa1-softirq/include/asm-ppc/softirq.h
--- 2.4.10pre2aa1/include/asm-ppc/softirq.h Sat Jul 21 00:04:30 2001
+++ 2.4.10pre2aa1-softirq/include/asm-ppc/softirq.h Thu Aug 30 00:23:09 2001
@@ -28,8 +28,6 @@
} \
} while (0)

-#define __cpu_raise_softirq(cpu, nr) set_bit((nr), &softirq_pending(cpu));
-
#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

#endif /* __ASM_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-s390/softirq.h 2.4.10pre2aa1-softirq/include/asm-s390/softirq.h
--- 2.4.10pre2aa1/include/asm-s390/softirq.h Thu Aug 16 22:03:40 2001
+++ 2.4.10pre2aa1-softirq/include/asm-s390/softirq.h Thu Aug 30 00:23:12 2001
@@ -36,8 +36,6 @@
do_softirq(); \
} while (0)

-#define __cpu_raise_softirq(cpu, nr) (softirq_pending(cpu) |= (1<<nr))
-
#endif /* __ASM_SOFTIRQ_H */

diff -urN 2.4.10pre2aa1/include/asm-s390x/softirq.h 2.4.10pre2aa1-softirq/include/asm-s390x/softirq.h
--- 2.4.10pre2aa1/include/asm-s390x/softirq.h Thu Aug 16 22:03:40 2001
+++ 2.4.10pre2aa1-softirq/include/asm-s390x/softirq.h Thu Aug 30 00:23:14 2001
@@ -36,8 +36,6 @@
do_softirq(); \
} while (0)

-#define __cpu_raise_softirq(cpu, nr) (softirq_pending(cpu) |= (1<<nr))
-
#endif /* __ASM_SOFTIRQ_H */

diff -urN 2.4.10pre2aa1/include/asm-sh/softirq.h 2.4.10pre2aa1-softirq/include/asm-sh/softirq.h
--- 2.4.10pre2aa1/include/asm-sh/softirq.h Sat Jul 21 00:04:31 2001
+++ 2.4.10pre2aa1-softirq/include/asm-sh/softirq.h Thu Aug 30 00:23:17 2001
@@ -25,8 +25,6 @@
} \
} while (0)

-#define __cpu_raise_softirq(cpu, nr) set_bit((nr), &softirq_pending(cpu));
-
#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

#endif /* __ASM_SH_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-sparc/softirq.h 2.4.10pre2aa1-softirq/include/asm-sparc/softirq.h
--- 2.4.10pre2aa1/include/asm-sparc/softirq.h Sat Jul 21 00:04:31 2001
+++ 2.4.10pre2aa1-softirq/include/asm-sparc/softirq.h Thu Aug 30 00:23:46 2001
@@ -22,13 +22,6 @@
__sti(); \
} \
} while (0)
-#define __do_cpu_raise_softirq(cpu, nr) (softirq_pending(cpu) |= (1<<nr))
-#define __cpu_raise_softirq(cpu, nr) \
-do { unsigned long flags; \
- local_irq_save(flags); \
- __do_cpu_raise_softirq(cpu, nr); \
- local_irq_restore(flags); \
-} while (0)
#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

#endif /* __SPARC_SOFTIRQ_H */
diff -urN 2.4.10pre2aa1/include/asm-sparc64/softirq.h 2.4.10pre2aa1-softirq/include/asm-sparc64/softirq.h
--- 2.4.10pre2aa1/include/asm-sparc64/softirq.h Sat Jul 21 00:04:31 2001
+++ 2.4.10pre2aa1-softirq/include/asm-sparc64/softirq.h Thu Aug 30 00:23:54 2001
@@ -20,13 +20,6 @@
} \
} while (0)

-#define __do_cpu_raise_softirq(cpu, nr) (softirq_pending(cpu) |= (1<<nr))
-#define __cpu_raise_softirq(cpu,nr) \
-do { unsigned long flags; \
- local_irq_save(flags); \
- __do_cpu_raise_softirq(cpu, nr); \
- local_irq_restore(flags); \
-} while (0)
#define in_softirq() (local_bh_count(smp_processor_id()) != 0)

#endif /* !(__SPARC64_SOFTIRQ_H) */
diff -urN 2.4.10pre2aa1/include/linux/interrupt.h 2.4.10pre2aa1-softirq/include/linux/interrupt.h
--- 2.4.10pre2aa1/include/linux/interrupt.h Wed Aug 29 15:05:25 2001
+++ 2.4.10pre2aa1-softirq/include/linux/interrupt.h Thu Aug 30 00:22:13 2001
@@ -74,6 +74,7 @@
asmlinkage void do_softirq(void);
extern void open_softirq(int nr, void (*action)(struct softirq_action*), void *data);
extern void softirq_init(void);
+#define __cpu_raise_softirq(cpu, nr) do { softirq_pending(cpu) |= 1UL << (nr); } while (0)
extern void FASTCALL(cpu_raise_softirq(unsigned int cpu, unsigned int nr));
extern void FASTCALL(raise_softirq(unsigned int nr));

diff -urN 2.4.10pre2aa1/kernel/softirq.c 2.4.10pre2aa1-softirq/kernel/softirq.c
--- 2.4.10pre2aa1/kernel/softirq.c Sat Aug 11 08:04:32 2001
+++ 2.4.10pre2aa1-softirq/kernel/softirq.c Thu Aug 30 00:24:09 2001
@@ -108,6 +108,9 @@
local_irq_restore(flags);
}

+/*
+ * This function must run with irq disabled!
+ */
inline void cpu_raise_softirq(unsigned int cpu, unsigned int nr)
{
__cpu_raise_softirq(cpu, nr);
@@ -127,7 +130,11 @@

void raise_softirq(unsigned int nr)
{
+ long flags;
+
+ local_irq_save(flags);
cpu_raise_softirq(smp_processor_id(), nr);
+ local_irq_restore(flags);
}

void open_softirq(int nr, void (*action)(struct softirq_action*), void *data)
@@ -195,8 +202,8 @@
local_irq_disable();
t->next = tasklet_vec[cpu].list;
tasklet_vec[cpu].list = t;
- local_irq_enable();
__cpu_raise_softirq(cpu, TASKLET_SOFTIRQ);
+ local_irq_enable();
}
}

@@ -229,8 +236,8 @@
local_irq_disable();
t->next = tasklet_hi_vec[cpu].list;
tasklet_hi_vec[cpu].list = t;
- local_irq_enable();
__cpu_raise_softirq(cpu, HI_SOFTIRQ);
+ local_irq_enable();
}
}

diff -urN 2.4.10pre2aa1/net/core/dev.c 2.4.10pre2aa1-softirq/net/core/dev.c
--- 2.4.10pre2aa1/net/core/dev.c Sat Aug 11 08:04:32 2001
+++ 2.4.10pre2aa1-softirq/net/core/dev.c Thu Aug 30 00:24:36 2001
@@ -1217,10 +1217,9 @@
enqueue:
dev_hold(skb->dev);
__skb_queue_tail(&queue->input_pkt_queue,skb);
- local_irq_restore(flags);
-
/* Runs from irqs or BH's, no need to wake BH */
__cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
+ local_irq_restore(flags);
#ifndef OFFLINE_SAMPLE
get_sample_stats(this_cpu);
#endif
@@ -1529,10 +1528,9 @@

local_irq_disable();
netdev_rx_stat[this_cpu].time_squeeze++;
- local_irq_enable();
-
/* This already runs in BH context, no need to wake up BH's */
__cpu_raise_softirq(this_cpu, NET_RX_SOFTIRQ);
+ local_irq_enable();

NET_PROFILE_LEAVE(softnet_process);
return;

Andrea
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