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Message-ID: <aKMbekefL4mJ23kW@localhost>
Date: Mon, 18 Aug 2025 14:24:26 +0200
From: Miroslav Lichvar <mlichvar@...hat.com>
To: Kurt Kanzenbach <kurt@...utronix.de>
Cc: Tony Nguyen <anthony.l.nguyen@...el.com>,
Przemek Kitszel <przemyslaw.kitszel@...el.com>,
Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Richard Cochran <richardcochran@...il.com>,
Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [Intel-wired-lan] [PATCH iwl-next] igb: Retrieve Tx timestamp
directly from interrupt
On Fri, Aug 15, 2025 at 08:50:23AM +0200, Kurt Kanzenbach wrote:
> Retrieve Tx timestamp directly from interrupt handler.
>
> The current implementation uses schedule_work() which is executed by the
> system work queue to retrieve Tx timestamps. This increases latency and can
> lead to timeouts in case of heavy system load.
>
> Therefore, fetch the timestamp directly from the interrupt handler.
>
> The work queue code stays for the Intel 82576. Tested on Intel i210.
I tested this patch on 6.17-rc1 with an Intel I350 card on a NTP
server (chrony 4.4), measuring packet rates and TX timestamp accuracy
with ntpperf. While the HW TX timestamping seems more reliable at some
lower request rates, there seems to be about 40% drop in the overall
performance of the server in how much requests it can handle (falling
back to SW timestamps when HW timestamp is missed). Is this expected
or something to be considered?
Before:
| responses | TX timestamp offset (ns)
rate clients | lost invalid basic xleave | min mean max stddev
1000 100 0.00% 0.00% 0.00% 100.00% -77 -42 +1 14
1050 105 0.00% 0.00% 0.00% 100.00% -68 -35 +2 13
1102 110 0.00% 0.00% 0.00% 100.00% -60 -14 +27 15
1157 115 0.00% 0.00% 0.00% 100.00% -28 +12 +53 14
1214 121 0.00% 0.00% 0.00% 100.00% -3 +34 +68 13
1274 127 0.00% 0.00% 0.00% 100.00% -5 +35 +70 14
1337 133 0.00% 0.00% 0.00% 100.00% -2 +30 +64 13
1403 140 0.00% 0.00% 0.00% 100.00% -27 +11 +57 14
1473 147 0.00% 0.00% 0.00% 100.00% -15 +27 +65 15
1546 154 0.00% 0.00% 0.00% 100.00% -56 -8 +41 18
1623 162 0.00% 0.00% 0.00% 100.00% -69 -27 +28 17
1704 170 0.00% 0.00% 0.00% 100.00% -39 -5 +30 13
1789 178 0.00% 0.00% 0.00% 100.00% -32 +3 +37 13
1878 187 0.00% 0.00% 0.00% 100.00% -22 +20 +75 18
1971 197 0.00% 0.00% 0.00% 100.00% -27 +6 +40 12
2069 206 0.00% 0.00% 0.00% 100.00% -22 +19 +62 15
2172 217 0.00% 0.00% 0.00% 100.00% +16 +53 +92 13
2280 228 0.00% 0.00% 0.00% 100.00% -30 +55 +92 18
2394 239 0.00% 0.00% 0.00% 100.00% -61 -5 +33 18
2513 251 0.00% 0.00% 0.00% 100.00% -66 -23 +20 14
2638 263 0.00% 0.00% 0.00% 100.00% -34 -1 +32 12
2769 276 0.00% 0.00% 0.00% 100.00% -20 +20 +60 14
2907 290 0.00% 0.00% 0.00% 100.00% -35 +6 +68 20
3052 305 0.00% 0.00% 0.00% 100.00% -29 +5 +40 12
3204 320 0.00% 0.00% 0.00% 100.00% -25 +8 +42 12
3364 336 0.00% 0.00% 0.00% 100.00% -12 +31 +70 14
3532 353 0.00% 0.00% 0.00% 100.00% -12 +31 +88 17
3708 370 0.00% 0.00% 0.00% 100.00% +4 +40 +80 13
3893 389 0.00% 0.00% 0.00% 100.00% -47 +42 +93 28
4087 408 0.00% 0.00% 0.00% 100.00% -63 -25 +33 18
4291 429 0.00% 0.00% 0.00% 100.00% -57 -8 +37 15
4505 450 0.00% 0.00% 0.00% 100.00% -8 +27 +64 13
4730 473 0.00% 0.00% 0.00% 100.00% +5 +44 +81 13
4966 496 0.00% 0.00% 0.00% 100.00% -30 +14 +11670 119
5214 521 0.00% 0.00% 0.00% 100.00% -36 +2 +18077 251
5474 547 0.00% 0.00% 0.00% 100.00% -30 +14 +16652 160
5747 574 0.00% 0.00% 0.00% 100.00% -15 +37 +18081 292
6034 603 0.00% 0.00% 0.00% 100.00% +8 +51 +16561 151
6335 633 0.00% 0.00% 0.00% 100.00% -10 +28 +18073 161
6651 665 0.00% 0.00% 0.00% 100.00% -23 +23 +16349 158
6983 698 0.00% 0.00% 0.00% 100.00% -26 +26 +78 19
7332 733 0.00% 0.00% 0.00% 100.00% -50 -10 +30 13
7698 769 0.00% 0.00% 0.00% 100.00% +5 +45 +16397 148
8082 808 0.00% 0.00% 0.00% 100.00% +17 +60 +18089 284
8486 848 0.00% 0.00% 0.00% 100.00% -46 +30 +18197 195
8910 891 0.00% 0.00% 0.00% 100.00% -48 -13 +16493 127
9355 935 0.00% 0.00% 0.00% 100.00% -34 +15 +18049 225
9822 982 0.00% 0.00% 0.00% 100.00% -4 +33 +16663 148
10313 1031 0.00% 0.00% 0.00% 100.00% -31 +22 +15046 110
10828 1082 0.00% 0.00% 0.00% 100.00% -14 +30 +18201 214
11369 1136 0.00% 0.00% 0.00% 100.00% +0 +44 +16464 171
11937 1193 0.00% 0.00% 0.00% 100.00% -7 +55 +18101 346
12533 1253 0.00% 0.00% 0.00% 100.00% -21 +22 +18113 372
13159 1315 0.00% 0.00% 0.00% 100.00% -18 +22 +18068 263
13816 1381 0.00% 0.00% 0.00% 100.00% -33 +17 +18032 171
14506 1450 0.00% 0.00% 0.00% 100.00% -49 -4 +18040 218
15231 1523 0.00% 0.00% 0.00% 100.00% -40 -1 +18171 224
15992 1599 0.00% 0.00% 0.00% 100.00% -24 +17 +18106 210
16791 1679 0.00% 0.00% 0.00% 100.00% +2 +45 +17998 219
17630 1763 0.00% 0.00% 0.00% 100.00% -78 -26 +16597 214
18511 1851 0.00% 0.00% 0.00% 100.00% -40 +5 +18087 238
19436 1943 0.00% 0.00% 0.00% 100.00% -33 +27 +18110 316
20407 2040 0.00% 0.00% 0.00% 100.00% -4 +57 +18132 359
21427 2142 0.00% 0.00% 0.00% 100.00% -21 +39 +18131 402
22498 2249 0.00% 0.00% 0.00% 100.00% -53 +50 +18109 478
23622 2362 0.00% 0.00% 0.00% 100.00% -23 +109 +18153 718
24803 2480 0.00% 0.00% 0.00% 100.00% -13 +680 +18113 2227
26043 2604 0.00% 0.00% 0.00% 100.00% -248 +4060 +18732 6280
27345 2734 0.00% 0.00% 0.00% 100.00% -35 +1139 +18072 2774
28712 2871 0.00% 0.00% 0.00% 100.00% +9 +1338 +18153 2828
30147 3014 0.00% 0.00% 0.00% 100.00% +29 +1481 +17354 3083
31654 3165 0.00% 0.00% 0.00% 100.00% -37 +1609 +18032 3405
33236 3323 0.00% 0.00% 0.00% 100.00% -97 +2092 +18050 4248
34897 3489 0.00% 0.00% 0.00% 100.00% -122 +2537 +18113 4933
36641 3664 0.00% 0.00% 0.00% 100.00% -117 +3943 +18433 5985
38473 3847 0.00% 0.00% 0.00% 100.00% -178 +4307 +18708 6488
40396 4039 0.00% 0.00% 0.00% 100.00% +61 +3570 +18272 5927
42415 4241 0.00% 0.00% 0.00% 100.00% -171 +5080 +18745 6633
44535 4453 0.00% 0.00% 0.00% 100.00% -620 +3489 +18162 5717
46761 4676 0.00% 0.00% 0.00% 100.00% -667 +2999 +18110 5335
49099 4909 0.00% 0.00% 0.00% 100.00% +28 +2867 +18219 5023
51553 5155 0.00% 0.00% 0.00% 100.00% +64 +2241 +18035 4339
54130 5413 0.00% 0.00% 0.00% 100.00% +11 +1873 +18097 3915
56836 5683 0.00% 0.00% 0.00% 100.00% -17 +1748 +17564 3828
59677 5967 0.00% 0.00% 0.00% 100.00% -13 +1786 +17458 3800
62660 6266 0.00% 0.00% 0.00% 100.00% -7 +1932 +18122 3905
65793 6579 0.00% 0.00% 0.00% 100.00% -29 +1831 +17546 3731
69082 6908 0.00% 0.00% 0.06% 99.94% -152 +2825 +18696 4125
72536 7253 0.00% 0.00% 0.00% 100.00% +233 +2128 +18188 3404
76162 7616 0.00% 0.00% 0.00% 100.00% +61 +2279 +18109 3774
79970 7997 0.00% 0.00% 0.00% 100.00% -26 +2256 +18108 3819
83968 8396 0.00% 0.00% 0.00% 100.00% -74 +1886 +17372 3276
88166 8816 0.00% 0.00% 0.05% 99.95% -77 +1570 +17911 2158
92574 9257 0.00% 0.00% 0.02% 99.98% -151 +1368 +18671 1848
97202 9720 0.00% 0.00% 0.00% 100.00% +40 +1418 +17280 2003
102062 10206 0.00% 0.00% 0.00% 100.00% +70 +1738 +17183 2442
107165 10716 0.00% 0.00% 0.00% 100.00% +3 +1784 +17451 2487
112523 11252 0.00% 0.00% 0.00% 100.00% -29 +1459 +16843 1623
118149 11814 0.00% 0.00% 0.00% 100.00% -14 +1438 +16975 1516
124056 12405 0.00% 0.00% 0.00% 100.00% -8 +1639 +17178 2050
130258 13025 0.00% 0.00% 0.00% 100.00% -39 +1607 +17312 1735
136770 13677 0.00% 0.00% 0.00% 100.00% -49 +1546 +18063 1553
143608 14360 0.00% 0.00% 0.00% 100.00% -28 +1602 +17486 1510
150788 15078 0.00% 0.00% 0.00% 100.00% -3 +1540 +16739 1364
158327 15832 0.05% 0.00% 0.16% 99.79% -108 +2111 +18784 1405
166243 16384 0.17% 0.00% 0.00% 99.83% +67 +1766 +18211 1235
174555 16384 0.00% 0.00% 0.00% 100.00% +50 +1702 +16643 1165
183282 16384 0.00% 0.00% 0.00% 100.00% -12 +1672 +16543 1196
192446 16384 0.00% 0.00% 0.00% 100.00% -28 +1697 +16716 1197
202068 16384 0.00% 0.00% 0.00% 100.00% -59 +1692 +16631 1179
212171 16384 0.00% 0.00% 0.00% 100.00% -49 +1767 +16621 1179
222779 16384 0.16% 0.00% 0.07% 99.77% -44 +1820 +16643 1147
233917 16384 3.60% 0.00% 0.20% 96.20% -131 +1680 +31346 1089
245612 16384 7.58% 0.00% 0.32% 92.10% -149 +2102 +86219 1316
257892 16384 11.15% 0.00% 0.40% 88.45% +14 +2265 +21315 1351
270786 16384 15.75% 0.00% 0.50% 83.75% +1 +2338 +18161 1394
284325 16384 19.72% 0.00% 0.60% 79.68% -52 +2387 +40370 1437
298541 16384 22.83% 0.00% 0.66% 76.51% -61 +2461 +21356 1467
313468 16384 26.26% 0.00% 0.70% 73.04% -38 +2495 +24987 1466
329141 16384 29.02% 0.00% 0.75% 70.24% -24 +2598 +25469 1484
345598 16384 32.21% 0.00% 0.78% 67.02% -1 +2636 +24568 1489
362877 16384 35.26% 0.00% 0.80% 63.94% -38 +2654 +21299 1495
381020 16384 38.66% 0.00% 0.96% 60.38% -85 +2392 +20972 1415
400071 16384 41.41% 0.00% 1.02% 57.57% -524 +2323 +20943 1508
420074 16384 43.53% 0.00% 1.09% 55.38% -656 +2464 +68387 1564
After:
| responses | TX timestamp offset (ns)
rate clients | lost invalid basic xleave | min mean max stddev
1000 100 0.00% 0.00% 0.00% 100.00% -50 -1 +60 25
1050 105 0.00% 0.00% 0.00% 100.00% -59 -25 +14 13
1102 110 0.00% 0.00% 0.00% 100.00% -36 +4 +36 13
1157 115 0.00% 0.00% 0.00% 100.00% -26 +20 +67 16
1214 121 0.00% 0.00% 0.00% 100.00% +11 +49 +85 14
1274 127 0.00% 0.00% 0.00% 100.00% -40 +36 +93 33
1337 133 0.00% 0.00% 0.00% 100.00% -37 +4 +49 17
1403 140 0.00% 0.00% 0.00% 100.00% -37 +9 +49 14
1473 147 0.00% 0.00% 0.00% 100.00% -54 -14 +25 14
1546 154 0.00% 0.00% 0.00% 100.00% -52 +9 +48 16
1623 162 0.00% 0.00% 0.00% 100.00% -35 +7 +50 15
1704 170 0.00% 0.00% 0.00% 100.00% -34 +1 +36 13
1789 178 0.00% 0.00% 0.00% 100.00% -44 -8 +31 13
1878 187 0.00% 0.00% 0.00% 100.00% -73 -33 +10 14
1971 197 0.00% 0.00% 0.00% 100.00% -76 -40 +0 14
2069 206 0.00% 0.00% 0.00% 100.00% -62 -4 +38 17
2172 217 0.00% 0.00% 0.00% 100.00% -11 +28 +68 15
2280 228 0.00% 0.00% 0.00% 100.00% +3 +47 +92 15
2394 239 0.00% 0.00% 0.00% 100.00% -19 +47 +95 22
2513 251 0.00% 0.00% 0.00% 100.00% -11 +22 +58 13
2638 263 0.00% 0.00% 0.00% 100.00% -45 -5 +56 15
2769 276 0.00% 0.00% 0.00% 100.00% -47 -10 +29 13
2907 290 0.00% 0.00% 0.00% 100.00% -26 +13 +57 14
3052 305 0.00% 0.00% 0.00% 100.00% -7 +34 +69 13
3204 320 0.00% 0.00% 0.00% 100.00% -91 -16 +25 17
3364 336 0.00% 0.00% 0.00% 100.00% -96 -45 +34 26
3532 353 0.00% 0.00% 0.00% 100.00% -36 +13 +60 18
3708 370 0.00% 0.00% 0.00% 100.00% -41 +2 +49 18
3893 389 0.00% 0.00% 0.00% 100.00% +1 +43 +87 14
4087 408 0.00% 0.00% 0.00% 100.00% +24 +69 +117 16
4291 429 0.00% 0.00% 0.00% 100.00% +43 +88 +137 15
4505 450 0.00% 0.00% 0.00% 100.00% -37 +19 +79 27
4730 473 0.00% 0.00% 0.00% 100.00% -20 +34 +11484 119
4966 496 0.00% 0.00% 0.00% 100.00% -47 +11 +57 21
5214 521 0.00% 0.00% 0.00% 100.00% -83 -29 +4438 49
5474 547 0.00% 0.00% 0.00% 100.00% -80 +5 +10236 105
5747 574 0.00% 0.00% 0.00% 100.00% -22 +27 +95 22
6034 603 0.00% 0.00% 0.00% 100.00% -11 +35 +16445 212
6335 633 0.00% 0.00% 0.00% 100.00% -44 -9 +29 13
6651 665 0.00% 0.00% 0.00% 100.00% -30 +19 +16177 141
6983 698 0.00% 0.00% 0.00% 100.00% +20 +64 +2875 28
7332 733 0.00% 0.00% 0.00% 100.00% +19 +78 +16312 136
7698 769 0.00% 0.00% 0.00% 100.00% -48 +33 +16456 137
8082 808 0.00% 0.00% 0.00% 100.00% -48 -4 +32 14
8486 848 0.00% 0.00% 0.00% 100.00% -23 +15 +52 13
8910 891 0.00% 0.00% 0.00% 100.00% -7 +32 +2514 23
9355 935 0.00% 0.00% 0.00% 100.00% -33 +24 +9744 74
9822 982 0.00% 0.00% 0.00% 100.00% -23 +18 +16182 227
10313 1031 0.00% 0.00% 0.00% 100.00% -36 +4 +16439 135
10828 1082 0.00% 0.00% 0.00% 100.00% -14 +30 +16198 177
11369 1136 0.00% 0.00% 0.00% 100.00% +4 +53 +16298 144
11937 1193 0.00% 0.00% 0.00% 100.00% +5 +45 +16296 164
12533 1253 0.00% 0.00% 0.00% 100.00% -27 +23 +16488 173
13159 1315 0.00% 0.00% 0.00% 100.00% -18 +24 +16318 135
13816 1381 0.00% 0.00% 0.00% 100.00% -9 +40 +16615 143
14506 1450 0.00% 0.00% 0.00% 100.00% -35 +18 +16327 155
15231 1523 0.00% 0.00% 0.00% 100.00% -36 +3 +16232 153
15992 1599 0.00% 0.00% 0.00% 100.00% -31 +12 +16371 148
16791 1679 0.00% 0.00% 0.00% 100.00% -29 +15 +16443 195
17630 1763 0.00% 0.00% 0.00% 100.00% -9 +30 +16399 188
18511 1851 0.00% 0.00% 0.00% 100.00% +3 +2039 +18611 5296
19436 1943 0.00% 0.00% 0.00% 100.00% -101 +1658 +18800 4692
20407 2040 0.00% 0.00% 0.00% 100.00% +23 +120 +16389 217
21427 2142 0.00% 0.00% 0.00% 100.00% -28 +126 +16177 331
22498 2249 0.00% 0.00% 0.00% 100.00% -21 +150 +16525 738
23622 2362 0.00% 0.00% 0.00% 100.00% +9 +293 +16218 1254
24803 2480 0.00% 0.00% 0.00% 100.00% -40 +322 +16404 1423
26043 2604 0.00% 0.00% 0.00% 100.00% -49 +389 +16426 1676
27345 2734 0.00% 0.00% 0.00% 100.00% -51 +691 +16498 2505
28712 2871 0.00% 0.00% 0.00% 100.00% -51 +963 +16607 3015
30147 3014 0.00% 0.00% 0.00% 100.00% -19 +1199 +16634 3397
31654 3165 0.00% 0.00% 0.00% 100.00% +10 +1592 +16675 3920
33236 3323 0.00% 0.00% 0.00% 100.00% -37 +1437 +16766 3881
34897 3489 0.00% 0.00% 0.00% 100.00% -34 +1031 +16765 3421
36641 3664 0.00% 0.00% 0.00% 100.00% -31 +308 +16668 1906
38473 3847 0.00% 0.00% 0.00% 100.00% -28 +327 +16841 1985
40396 4039 0.00% 0.00% 0.00% 100.00% -11 +570 +16775 2738
42415 4241 0.00% 0.00% 0.00% 100.00% -24 +392 +16872 2225
44535 4453 0.00% 0.00% 0.00% 100.00% -12 +396 +17011 2146
46761 4676 0.00% 0.00% 0.00% 100.00% -28 +406 +17292 2061
49099 4909 0.00% 0.00% 0.00% 100.00% -43 +425 +17224 2025
51553 5155 0.00% 0.00% 0.00% 100.00% -26 +578 +17207 2192
54130 5413 0.00% 0.00% 0.00% 100.00% -22 +703 +17214 2254
56836 5683 0.00% 0.00% 0.00% 100.00% -9 +780 +17239 2192
59677 5967 0.00% 0.00% 0.00% 100.00% -41 +1194 +17258 2931
62660 6266 0.00% 0.00% 0.00% 100.00% -51 +1245 +17285 3066
65793 6579 0.00% 0.00% 0.00% 100.00% -64 +1247 +17246 3103
69082 6908 0.00% 0.00% 0.00% 100.00% -784 +2074 +18422 3355
72536 7253 0.00% 0.00% 0.00% 100.00% -982 +660 +16681 1700
76162 7616 0.00% 0.00% 0.00% 100.00% +0 +1462 +17309 2513
79970 7997 0.00% 0.00% 0.00% 100.00% +280 +3833 +17455 5181
83968 8396 0.00% 0.00% 0.00% 100.00% -26 +1047 +17189 1689
88166 8816 0.00% 0.00% 0.00% 100.00% -85 +835 +16783 1307
92574 9257 0.00% 0.00% 0.00% 100.00% -122 +803 +16628 1311
97202 9720 0.00% 0.00% 0.00% 100.00% -44 +947 +16791 1345
102062 10206 0.00% 0.00% 0.00% 100.00% +7 +1033 +16637 1349
107165 10716 0.01% 0.00% 0.00% 99.99% +7 +1002 +24510 1311
112523 11252 0.00% 0.00% 0.00% 100.00% +14 +1054 +16479 1281
118149 11814 0.00% 0.00% 0.11% 99.89% -170 +1560 +17766 1122
124056 12405 0.00% 0.00% 0.00% 100.00% +24 +1255 +16566 1230
130258 13025 0.00% 0.00% 0.00% 100.00% +28 +1218 +16479 1331
136770 13677 0.12% 0.00% 0.05% 99.82% -13 +1336 +16770 1586
143608 14360 3.35% 0.00% 0.23% 96.41% -31 +1547 +21513 1924
150788 15078 7.22% 0.00% 0.41% 92.37% -37 +1617 +25333 1989
158327 15832 11.59% 0.00% 0.62% 87.78% -44 +1757 +24397 2110
166243 16384 15.07% 0.00% 0.77% 84.16% -36 +2074 +21110 2345
174555 16384 19.09% 0.00% 0.92% 80.00% -45 +2109 +26063 2294
183282 16384 23.00% 0.00% 1.02% 75.98% -35 +2222 +153077 2407
192446 16384 26.77% 0.00% 1.14% 72.09% -41 +2267 +18813 2397
202068 16384 30.04% 0.00% 1.21% 68.74% -45 +2374 +23266 2413
212171 16384 32.80% 0.00% 1.34% 65.86% -49 +2563 +23285 2307
222779 16384 36.43% 0.00% 1.31% 62.26% -158 +2693 +26937 2346
233917 16384 39.76% 0.00% 1.38% 58.86% +85 +2848 +25018 2349
245612 16384 42.52% 0.00% 1.41% 56.07% +89 +2846 +153305 2409
257892 16384 44.83% 0.00% 1.41% 53.76% +14 +2789 +24800 2323
270786 16384 47.64% 0.00% 1.43% 50.94% -19 +2766 +25002 2382
284325 16384 49.02% 0.00% 1.51% 49.47% -886 +2687 +23521 2006
298541 16384 52.04% 0.00% 1.51% 46.44% -917 +3332 +118317 2057
--
Miroslav Lichvar
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