One - The Linux Kernel Archives

More documents

Recommendations

Info

248 • Linux Symposium 2004 • Volume One packet are the same. I doubt the MMIO reads and MMIO writes are the limiting factors. More likely DMA access to memory (and thus TX/RX descriptor rings) limits NIC packet processing. 4 Measuring Cache-line Misses The Event Address Registers 2 (EAR) can only record one event at a time. What is so interesting about them is that they record precise information about data cache misses. For instance for a data cache miss, you get the: • address of the instruction, likely a load • address of the target data • latency in cycles to resolve the miss The information pinpoints the source of the miss, not the consequence (i.e., the stall). The Data EAR (DEAR) can also tell us about MMIO reads via sampling. The DEAR can only record loads that miss, not stores. Of course, MMIO reads always miss because they are uncached. This is interesting if we want to track down which MMIO addresses are “hot.” It’s usually easier to track down usage in source code knowing which MMIO address is referenced. Collecting with DEAR sampling requires two parameters be tweaked to statistically improve the samples. One is the frequency at which Data Addresses are recorded and the other is the threshold (how many CPU cycles latency). Because we know the latency to L3 is about 21 cycles, setting the EAR threshold to a value higher (e.g., 64 cycles) ensures only the load 2 pfmon v3.1 is the first version to support EAR and is expected to be available in August, 2004. misses accessing main memory will be captured. This is how to select which level of cacheline misses one samples. While high threshholds (e.g., 64 cycles) will show us where the longest delays occur, it will not show us the worst offenders. Doing a second run with a lower threshold (e.g., 4 cycles) shows all L1, L2, and L3 cache misses and provides a much broader picture of cache utilization. When sampling events with low threshholds, we will get saturated with events and need to reduce the number of events actually sampled to every 5000th. The appropriate value will depend on the workload and how patient one is. The workload needs to be run long enough to be statistically significant and the sampling period needs to be high enough to not significantly perturb the workload. 4.1 tg3 Data Cache misses > 64 cycles For the output in Figure 8, I’ve iteratively decreased the smpl-periods until I noticed the total pktgen throughput starting to drop. Figure 8 output only shows the tg3 interrupt code path since pfmon is bound to CPU 0. Normally, it would be useful to run this again with cpu-list=1. We could then see what the TX code path and pktgen are doing. Also, the pin-command option in this example doesn’t do anything since pktgen-single-tg3 directs a pktgen kernel thread bound CPU 1 to do the real work. I’ve included the option only to make people aware of it. 4.2 tg3 Data Cache misses > 4 cycles Figure 9 puts the lat64 output in Figure 8 into better perspective. It shows tg3 is spending more time for L1 and L2 misses than L3 misses
Linux Symposium 2004 • Volume One • 249 gsyprf3:~# pfmon31 --us-c --cpu-list=0 --pin-command --resolve-addr \ --smpl-module=dear-hist-itanium2 \ -e data_ear_cache_lat64 --long-smpl-periods=500 \ --smpl-periods-random=0xfff:10 --system-wide \ -k -- /usr/src/pktgen-testing/pktgen-single-tg3 added event set 0 only kernel symbols are resolved in system-wide mode Adding devices to run. Configuring devices Running... ctrl^C to stop 57: 7209769 0 IO-SAPIC-level eth1 Result: OK: 5915877(c5845032+d70845) usec, 5000000 (64byte) 845308pps 412Mb/sec (432797696bps) errors: 0 57: 7827812 0 IO-SAPIC-level eth1 # total_samples 672 # instruction addr view # sorted by count # showing per per distinct value # %L2 : percentage of L1 misses that hit L2 # %L3 : percentage of L1 misses that hit L3 # %RAM : percentage of L1 misses that hit memory # L2 : 5 cycles load latency # L3 : 12 cycles load latency # sampling period: 500 #count %self %cum %L2 %L3 %RAM instruction addr 38 5.65% 5.65% 0.00% 0.00% 100.00% 0xa000000100009141 ia64_spinlock_contention +0x21 36 5.36% 11.01% 0.00% 0.00% 100.00% 0xa00000020003e580 tg3_interrupt[tg3]+0xe0 32 4.76% 15.77% 0.00% 0.00% 100.00% 0xa000000200034770 tg3_write_indirect_reg32[tg3] +0x90 32 4.76% 20.54% 0.00% 0.00% 100.00% 0xa00000020003e640 tg3_interrupt[tg3]+0x1a0 30 4.46% 25.00% 0.00% 0.00% 100.00% 0xa000000200034e91 tg3_enable_ints[tg3]+0x91 29 4.32% 29.32% 0.00% 0.00% 100.00% 0xa00000020003e510 tg3_interrupt[tg3]+0x70 28 4.17% 33.48% 0.00% 0.00% 100.00% 0xa00000020003d1a0 tg3_tx[tg3]+0x2e0 27 4.02% 37.50% 0.00% 0.00% 100.00% 0xa00000020003cfa0 tg3_tx[tg3]+0xe0 24 3.57% 41.07% 0.00% 0.00% 100.00% 0xa00000020003cfd1 tg3_tx[tg3]+0x111 21 3.12% 44.20% 0.00% 0.00% 100.00% 0xa000000200034e60 tg3_enable_ints[tg3]+0x60 . . . # level 0 : counts=0 avg_cycles=0.0ms 0.00% # level 1 : counts=0 avg_cycles=0.0ms 0.00% # level 2 : counts=672 avg_cycles=0.0ms 100.00% approx cost: 0.0s Figure 8: tg3 v3.6 lat64 output
Page 1:
Proceedings of the Linux Symposium
Page 4 and 5:
The State of ACPI in the Linux Kern
Page 7 and 8:
Conference Organizers Andrew J. Hut
Page 9 and 10:
TCP Connection Passing Werner Almes
Page 11 and 12:
Linux Symposium 2004 • Volume One
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Cooperative Linux Dan Aloni da-x@co
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Build your own Wireless Access Poin
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Run-time testing of LSB Application
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Linux Block IO—present and future
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Linux AIO Performance and Robustnes
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Methods to Improve Bootup Time in L
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Linux on NUMA Systems Martin J. Bli
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Improving Kernel Performance by Unm
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Linux Virtualization on IBM POWER5
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
The State of ACPI in the Linux Kern
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Scaling Linux® to the Extreme From
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Get More Device Drivers out of the
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Big Servers—2.6 compared to 2.4 W
Page 165 and 166:
Page 167 and 168:
Multi-processor and Frequency Scali
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Dynamic Kernel Module Support: From
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198: Linux Symposium 2004 • Volume One
Page 203 and 204: e100 Weight Reduction Program Writi
Page 207 and 208: NFSv4 and rpcsec_gss for linux J. B
Page 215 and 216: Comparing and Evaluating epoll, sel
Page 227 and 228: The (Re)Architecture of the X Windo
Page 239 and 240: IA64-Linux perf tools for IO dorks
Page 247: Linux Symposium 2004 • Volume One
Page 255 and 256: Carrier Grade Server Features in th
Page 269 and 270: Demands, Solutions, and Improvement
Page 287 and 288: Hotplug Memory and the Linux VM Dav
show all

One - The Linux Kernel Archives

Create successful ePaper yourself

Delete template?

Save as template?