Re: userspace irq balancer

James Cleverdon
2003-05-22T14:05:45Z

[-- Attachment #1: Type: text/plain, Size: 1065 bytes --]

On Wednesday 21 May 2003 07:04 pm, William Lee Irwin III wrote:
[ Snip! ]
> ...
> IMHO Linux on Pentium IV should use the TPR in conjunction with _very_
> simplistic interrupt load accounting by default and all more
> sophisticated logic should be punted straight to userspace as an
> administrative API.
>
[ Snip! ]
>
> i.e. frob the fscking TPR as recommended by the APIC docs every once in
> a while by default, punt anything (and everything) fancier up to
> userspace, and get the code that doesn't even understand what the fsck
> DESTMOD means the Hell out of the kernel and the Hell away from my
> IO-APIC RTE's.
>
>
> -- wli

Here's my old very stupid TPR patch . It lacks TPRing soft ints for kernel
preemption, etc. Because the xTPR logic only compares the top nibble of the
TPR and I don't want to mask out IRQs unnecessarily, it only tracks busy/idle
and IRQ/no-IRQ.

Simple enough for you, Bill? 8^)

--
James Cleverdon
IBM xSeries Linux Solutions
{jamesclv(Unix, preferred), cleverdj(Notes)} at us dot ibm dot com

[-- Attachment #2: tpr_dyn-2003-01-10_2.5.55 --]
[-- Type: text/x-diff, Size: 3480 bytes --]

diff -pru j55/arch/i386/kernel/irq.c t55/arch/i386/kernel/irq.c
--- j55/arch/i386/kernel/irq.c Wed Jan 8 20:03:51 2003
+++ t55/arch/i386/kernel/irq.c Fri Jan 10 18:01:03 2003
@@ -329,6 +329,7 @@ asmlinkage unsigned int do_IRQ(struct pt
struct irqaction * action;
unsigned int status;

+ apic_adj_tpr(TPR_IRQ);
irq_enter();

#ifdef CONFIG_DEBUG_STACKOVERFLOW
@@ -406,6 +407,7 @@ out:
spin_unlock(&desc->lock);

irq_exit();
+ apic_adj_tpr(-TPR_IRQ);

return 1;
}
diff -pru j55/arch/i386/kernel/process.c t55/arch/i386/kernel/process.c
--- j55/arch/i386/kernel/process.c Wed Jan 8 20:03:48 2003
+++ t55/arch/i386/kernel/process.c Fri Jan 10 17:59:13 2003
@@ -143,7 +143,9 @@ void cpu_idle (void)
irq_stat[smp_processor_id()].idle_timestamp = jiffies;
while (!need_resched())
idle();
+ apic_set_tpr(TPR_TASK);
schedule();
+ apic_set_tpr(TPR_IDLE);
}
}

diff -pru j55/include/asm-i386/apic.h t55/include/asm-i386/apic.h
--- j55/include/asm-i386/apic.h Wed Jan 8 20:04:27 2003
+++ t55/include/asm-i386/apic.h Fri Jan 10 17:59:13 2003
@@ -64,6 +64,22 @@ static inline void ack_APIC_irq(void)
apic_write_around(APIC_EOI, 0);
}

+static inline void apic_set_tpr(unsigned long val)
+{
+ unsigned long value;
+
+ value = apic_read(APIC_TASKPRI);
+ apic_write_around(APIC_TASKPRI, (value & ~APIC_TPRI_MASK) + val);
+}
+
+static inline void apic_adj_tpr(long adj)
+{
+ unsigned long value;
+
+ value = apic_read(APIC_TASKPRI);
+ apic_write_around(APIC_TASKPRI, value + adj);
+}
+
extern int get_maxlvt(void);
extern void clear_local_APIC(void);
extern void connect_bsp_APIC (void);
@@ -96,6 +112,15 @@ extern unsigned int nmi_watchdog;
#define NMI_LOCAL_APIC 2
#define NMI_INVALID 3

+#else /* CONFIG_X86_LOCAL_APIC */
+#define apic_set_tpr(val)
+#define apic_adj_tpr(adj)
#endif /* CONFIG_X86_LOCAL_APIC */

+/* Priority values for apic_adj_tpr() and apic_set_tpr() */
+/* xAPICs only do priority comparisons on the upper nibble. */
+#define TPR_IDLE (0x00L)
+#define TPR_TASK (0x10L)
+#define TPR_IRQ (0x10L)
+
#endif /* __ASM_APIC_H */
diff -pru j55/include/asm-i386/mach-summit/mach_apic.h t55/include/asm-i386/mach-summit/mach_apic.h
--- j55/include/asm-i386/mach-summit/mach_apic.h Fri Jan 10 16:16:44 2003
+++ t55/include/asm-i386/mach-summit/mach_apic.h Fri Jan 10 19:24:52 2003
@@ -4,7 +4,7 @@
extern int x86_summit;

#define esr_disable (1)
-#define no_balance_irq (0)
+#define no_balance_irq (1)

#define XAPIC_DEST_CPUS_MASK 0x0Fu
#define XAPIC_DEST_CLUSTER_MASK 0xF0u
@@ -13,7 +13,7 @@ extern int x86_summit;
((phys_apic) & XAPIC_DEST_CLUSTER_MASK) )

#define APIC_DFR_VALUE (x86_summit ? APIC_DFR_CLUSTER : APIC_DFR_FLAT)
-#define TARGET_CPUS (x86_summit ? XAPIC_DEST_CPUS_MASK : cpu_online_map)
+#define TARGET_CPUS (x86_summit ? xapic_round_robin_cpu_apic_id() : cpu_online_map)

#define APIC_BROADCAST_ID (x86_summit ? 0xFF : 0x0F)
#define check_apicid_used(bitmap, apicid) (0)
@@ -106,4 +106,20 @@ static inline int check_phys_apicid_pres
return (1);
}

+/*
+ * xapic_round_robin_cpu_apic_id -- Distribute the interrupts using a simple
+ * round robin scheme.
+ */
+static inline int xapic_round_robin_cpu_apic_id(void)
+{
+ int val;
+ static unsigned next_cpu = 0;
+
+ if (next_cpu >= NR_CPUS || cpu_2_logical_apicid[next_cpu] == BAD_APICID)
+ next_cpu = 0;
+ val = cpu_to_logical_apicid(next_cpu) | XAPIC_DEST_CPUS_MASK;
+ ++next_cpu;
+ return (val);
+}
+
#endif /* __ASM_MACH_APIC_H */