+++ /dev/null
-
-
-* Microbenchmarks
-
-Use timestamp counter to calculate the time spent, with interrupts disabled.
-Machine : Pentium 4 3GHz
-Fully preemptible kernel
-marker : MARK(subsys_mark1, "%d %p", 1, NULL);
-Linux Kernel Markers 0.19
-
-* Execute an empty loop
-NR_LOOPS : 10000000
-time delta (cycles): 15026497
-cycles per loop : 1.50
-- i386 "optimized" : immediate value, test and predicted branch
- (non connected marker)
-NR_LOOPS : 10000000
-time delta (cycles): 40031640
-cycles per loop : 4.00
-cycles per loop for marker : 2.50
-- i386 "generic" : load, test and predicted branch
- (non connected marker)
-NR_LOOPS : 10000000
-time delta (cycles): 26697878
-cycles per loop : 2.67
-cycles per loop for marker : 1.17
-
-* Execute a loop of memcpy 4096 bytes
-- Without marker
-NR_LOOPS : 10000
-time delta (cycles): 12981555
-cycles per loop : 1298.16
-- i386 "optimized" : immediate value, test and predicted branch
- (non connected marker)
-NR_LOOPS : 10000
-time delta (cycles): 12982290
-cycles per loop : 1298.23
-cycles per loop for marker : 0.074
-- i386 "generic" : load, test and predicted branch
- (non connected marker)
-NR_LOOPS : 10000
-time delta (cycles): 13002788
-cycles per loop : 1300.28
-cycles per loop for marker : 2.123
-
-
-The following tests are done with the "optimized" markers only
-
-Execute a loop with a marker enabled, with an empty probe.
-NR_LOOPS : 100000
-time delta (cycles): 5210587
-cycles per loop : 52.11
-cycles per loop for empty probe : 52.11-4.00=48.11
-
-Execute a loop with marker enabled, with i386 direct argument passing.
-NR_LOOPS : 100000
-time delta (cycles): 5299837
-cycles per loop : 53.00
-cycles per loop to get arguments in probe (from stack) on x86 : 53.00-52.11=0.89
-
-Execute a loop with marker enabled, with var args probe.
-NR_LOOPS : 100000
-time delta (cycles): 5574300
-cycles per loop : 55.74
-cycles per loop to get expected variable arguments on x86 : 55.74-53.00=2.74
-
-Execute a loop with marker enabled, with var args probe, format string
-processing.
-NR_LOOPS : 100000
-time delta (cycles): 9622117
-cycles per loop : 96.22
-cycles per loop to dynamically parse arguments
- with format string : 96.22-55.74=40.48
-
-
-* Assembly code
-
-
-- Optimized
-
-static int my_open(struct inode *inode, struct file *file)
-{
- 0: 55 push %ebp
- 1: 89 e5 mov %esp,%ebp
- 3: 83 ec 0c sub $0xc,%esp
- MARK(subsys_mark1, "%d %p", 1, NULL);
- 6: b0 00 mov $0x0,%al
- 8: 84 c0 test %al,%al
- a: 75 07 jne 13 <my_open+0x13>
-
- return -EPERM;
-}
- c: b8 ff ff ff ff mov $0xffffffff,%eax
- 11: c9 leave
- 12: c3 ret
- 13: b8 01 00 00 00 mov $0x1,%eax
- 18: e8 fc ff ff ff call 19 <my_open+0x19>
- 1d: c7 44 24 08 00 00 00 movl $0x0,0x8(%esp)
- 24: 00
- 25: c7 44 24 04 01 00 00 movl $0x1,0x4(%esp)
- 2c: 00
- 2d: c7 04 24 0d 00 00 00 movl $0xd,(%esp)
- 34: ff 15 74 10 00 00 call *0x1074
- 3a: b8 01 00 00 00 mov $0x1,%eax
- 3f: e8 fc ff ff ff call 40 <my_open+0x40>
- 44: eb c6 jmp c <my_open+0xc>
-
-
-- Generic
-
-static int my_open(struct inode *inode, struct file *file)
-{
- 0: 55 push %ebp
- 1: 89 e5 mov %esp,%ebp
- 3: 83 ec 0c sub $0xc,%esp
- MARK(subsys_mark1, "%d %p", 1, NULL);
- 6: 0f b6 05 20 10 00 00 movzbl 0x1020,%eax
- d: 84 c0 test %al,%al
- f: 75 07 jne 18 <my_open+0x18>
-
- return -EPERM;
-}
- 11: b8 ff ff ff ff mov $0xffffffff,%eax
- 16: c9 leave
- 17: c3 ret
- 18: b8 01 00 00 00 mov $0x1,%eax
- 1d: e8 fc ff ff ff call 1e <my_open+0x1e>
- 22: c7 44 24 08 00 00 00 movl $0x0,0x8(%esp)
- 29: 00
- 2a: c7 44 24 04 01 00 00 movl $0x1,0x4(%esp)
- 31: 00
- 32: c7 04 24 0d 00 00 00 movl $0xd,(%esp)
- 39: ff 15 74 10 00 00 call *0x1074
- 3f: b8 01 00 00 00 mov $0x1,%eax
- 44: e8 fc ff ff ff call 45 <my_open+0x45>
- 49: eb c6 jmp 11 <my_open+0x11>
-
-* Size (x86)
-
-- Optimized
-
-Adds 6 bytes in the "likely" path.
-Adds 32 bytes in the "unlikely" path.
-
-- Generic
-
-Adds 11 bytes in the "likely" path.
-Adds 32 bytes in the "unlikely" path.
-
-
-
-Conclusion
-
-In an empty loop, the generic marker is faster than the optimized marker. This
-may be due to better performances of the movzbl instruction over the movb on the
-Pentium 4 architecture. However, when we execute a loop of 4kB copy, the impact
-of the movzbl becomes greater because it uses the memory bandwidth.
-
-The preemption disabling and call to a probe itself costs 48.11 cycles, almost
-as much as dynamically parsing the format string to get the variable arguments
-(40.48 cycles).
-
-There is almost no difference, on x86, between passing the arguments directly on
-the stack and using a variable argument list when its layout is known
-statically (0.89 cycles vs 2.74 cycles).
-
-
-
projects / lttv.git / blobdiff