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authorTim Chen <tim.c.chen@linux.intel.com>2006-07-30 06:04:02 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-07-31 16:28:42 -0400
commit3c829c367a1a52550378584a657768217971e587 (patch)
tree78dfcbe28e6a0db56992ce5ad5891398a9743bf4
parent953a7f20667a8b6217ea2ac49c0877e957a0130a (diff)
[PATCH] Reducing local_bh_enable/disable overhead in irqtrace
The recent changes from irqtrace feature has added overheads to local_bh_disable and local_bh_enable that reduces UDP performance across x86_64 and IA64, even though IA64 does not support the irqtrace feature. Patch in question is [PATCH]lockdep: irqtrace subsystem, core http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=c ommit;h=de30a2b355ea85350ca2f58f3b9bf4e5bc007986 Prior to this patch, local_bh_disable was a short macro. Now it is a function which calls __local_bh_disable with added irq flags save and restore. The irq flags save and restore were also added to local_bh_enable, probably for injecting the trace irqs code. This overhead is on the generic code path across all architectures. On a IA_64 test machine (Itanium-2 1.6 GHz) running a benchmark like netperf's UDP streaming test, the added overhead results in a drop of 3% in throughput, as udp_sendmsg calls the local_bh_enable/disable several times. Other workloads that have heavy usages of local_bh_enable/disable could also be affected. The patch ideally should not have affected IA-64 performance as it does not have IRQ tracing support. A significant portion of the overhead is in the added irq flags save and restore, which I think is not needed if IRQ tracing is unused. A suggested patch is attached below that recovers the lost performance. However, the "ifdef"s in the patch are a bit ugly. Signed-off-by: Tim Chen <tim.c.chen@intel.com> Acked-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/softirq.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/softirq.c b/kernel/softirq.c
index aab880677ce0..3789ca98197c 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -65,6 +65,7 @@ static inline void wakeup_softirqd(void)
65 * This one is for softirq.c-internal use, 65 * This one is for softirq.c-internal use,
66 * where hardirqs are disabled legitimately: 66 * where hardirqs are disabled legitimately:
67 */ 67 */
68#ifdef CONFIG_TRACE_IRQFLAGS
68static void __local_bh_disable(unsigned long ip) 69static void __local_bh_disable(unsigned long ip)
69{ 70{
70 unsigned long flags; 71 unsigned long flags;
@@ -80,6 +81,13 @@ static void __local_bh_disable(unsigned long ip)
80 trace_softirqs_off(ip); 81 trace_softirqs_off(ip);
81 raw_local_irq_restore(flags); 82 raw_local_irq_restore(flags);
82} 83}
84#else /* !CONFIG_TRACE_IRQFLAGS */
85static inline void __local_bh_disable(unsigned long ip)
86{
87 add_preempt_count(SOFTIRQ_OFFSET);
88 barrier();
89}
90#endif /* CONFIG_TRACE_IRQFLAGS */
83 91
84void local_bh_disable(void) 92void local_bh_disable(void)
85{ 93{
@@ -121,12 +129,16 @@ EXPORT_SYMBOL(_local_bh_enable);
121 129
122void local_bh_enable(void) 130void local_bh_enable(void)
123{ 131{
132#ifdef CONFIG_TRACE_IRQFLAGS
124 unsigned long flags; 133 unsigned long flags;
125 134
126 WARN_ON_ONCE(in_irq()); 135 WARN_ON_ONCE(in_irq());
136#endif
127 WARN_ON_ONCE(irqs_disabled()); 137 WARN_ON_ONCE(irqs_disabled());
128 138
139#ifdef CONFIG_TRACE_IRQFLAGS
129 local_irq_save(flags); 140 local_irq_save(flags);
141#endif
130 /* 142 /*
131 * Are softirqs going to be turned on now: 143 * Are softirqs going to be turned on now:
132 */ 144 */
@@ -142,18 +154,22 @@ void local_bh_enable(void)
142 do_softirq(); 154 do_softirq();
143 155
144 dec_preempt_count(); 156 dec_preempt_count();
157#ifdef CONFIG_TRACE_IRQFLAGS
145 local_irq_restore(flags); 158 local_irq_restore(flags);
159#endif
146 preempt_check_resched(); 160 preempt_check_resched();
147} 161}
148EXPORT_SYMBOL(local_bh_enable); 162EXPORT_SYMBOL(local_bh_enable);
149 163
150void local_bh_enable_ip(unsigned long ip) 164void local_bh_enable_ip(unsigned long ip)
151{ 165{
166#ifdef CONFIG_TRACE_IRQFLAGS
152 unsigned long flags; 167 unsigned long flags;
153 168
154 WARN_ON_ONCE(in_irq()); 169 WARN_ON_ONCE(in_irq());
155 170
156 local_irq_save(flags); 171 local_irq_save(flags);
172#endif
157 /* 173 /*
158 * Are softirqs going to be turned on now: 174 * Are softirqs going to be turned on now:
159 */ 175 */
@@ -169,7 +185,9 @@ void local_bh_enable_ip(unsigned long ip)
169 do_softirq(); 185 do_softirq();
170 186
171 dec_preempt_count(); 187 dec_preempt_count();
188#ifdef CONFIG_TRACE_IRQFLAGS
172 local_irq_restore(flags); 189 local_irq_restore(flags);
190#endif
173 preempt_check_resched(); 191 preempt_check_resched();
174} 192}
175EXPORT_SYMBOL(local_bh_enable_ip); 193EXPORT_SYMBOL(local_bh_enable_ip);