System.Tests.Perf_DateTime.GetNow gets slower every summer due to daylight savings

[dakersnar]

System.Tests.Perf_DateTime.GetNow has regressed across multiple configurations.

Reporting System:

Looking at the commit diff, #66282 seems to be to blame.

Repro:

git clone https://github.com/dotnet/performance.git
py .\performance\scripts\benchmarks_monthly.py net7.0-preview2 net7.0-preview3 --filter System.Tests.Perf_DateTime.GetNow 

## System.Tests.Perf_DateTime.GetNow

Result	Base	Diff	Ratio	Operating System	Bit	Processor Name
Same	112.05	114.53	0.98	Windows 10	X64	Intel Xeon CPU E5-1650 v4 3.60GHz
Same	93.72	99.81	0.94	Windows 11	X64	AMD Ryzen Threadripper PRO 3945WX 12-Cores
Slower	73.98	83.75	0.88	Windows 11	X64	AMD Ryzen 9 5900X
Same	131.78	149.14	0.88	Windows 11	X64	Intel Core i5-4300U CPU 1.90GHz (Haswell)
Same	118.61	116.32	1.02	Windows 11	X64	Unknown processor
Same	88.62	86.35	1.03	Windows 11	X64	Intel Core i7-8700 CPU 3.20GHz (Coffee Lake)
Same	103.63	99.92	1.04	Windows 11	X64	Intel Core i9-9900T CPU 2.10GHz
Same	372.20	380.11	0.98	alpine 3.13	X64	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Same	66.48	65.91	1.01	centos 7	X64	Intel Xeon CPU E5530 2.40GHz
Slower	416.66	472.23	0.88	debian 11	X64	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Slower	70.55	139.81	0.50	ubuntu 18.04	X64	Intel Xeon CPU E5-1650 v4 3.60GHz
Same	198.80	190.36	1.04	ubuntu 18.04	X64	Intel Core i7-2720QM CPU 2.20GHz (Sandy Bridge)
Same	240.11	241.49	0.99	alpine 3.12	Arm64	Unknown processor
Same	243.79	242.33	1.01	ubuntu 18.04	Arm64	Unknown processor
Slower	169.90	191.41	0.89	Windows 10	Arm64	Microsoft SQ1 3.0 GHz
Slower	169.84	194.79	0.87	Windows 11	Arm64	Microsoft SQ1 3.0 GHz
Same	403.45	402.18	1.00	Windows 10	X86	Intel Xeon CPU E5-1650 v4 3.60GHz
Slower	244.43	272.36	0.90	Windows 11	X86	AMD Ryzen Threadripper PRO 3945WX 12-Cores
Same	669.31	771.68	0.87	Windows 11	X86	Intel Core i7-10510U CPU 1.80GHz
Same	294.33	296.09	0.99	Windows 7 SP1	X86	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Same	766.67	714.33	1.07	ubuntu 18.04	Arm	ARMv7 Processor rev 3 (v7l)
Slower	1358.46	1709.54	0.79	Windows 10	Arm	Microsoft SQ1 3.0 GHz
Slower	94.22	169.26	0.56	macOS Monterey 12.2.1	X64	Intel Core i7-5557U CPU 3.10GHz (Broadwell)
Same	162.60	158.64	1.02	macOS Monterey 12.3.1	X64	Intel Core i7-4870HQ CPU 2.50GHz (Haswell)

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[EgorBo]

This is expected, DateTime.Now regresses and improves once a year at fixed dates due to DST ;-) https://twitter.com/EgorBo/status/1460697206667763714

[danmoseley]

this code only runs when we're in DST: https://github.com/dotnet/runtime/blob/67761043f1b0e1514a1b8c1c6d99a353737a24a1/src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs#L1383-L1412

But, that doesn't seem like much. would need profiling.

[EgorBo]

@danmoseley I don't think it executes that code as part of DateTime.Now, I assume the regression is internal in kernel32

[EgorBo]

oh, or maybe it does?

[danmoseley]

Is that with DST, or without? If GetDatePart is larger in DST, then it's perhaps because it's getting Year out of the DateTime in that block. The code before already gets Day and Month and Year, though. I wonder if there is opportunity to have GetDatePart() return all of those together rather than repeat its work. (Edit - I see that's GetDate())

is the codegen for GetDatePart() reasonable?

[EgorBo]

Ah, ignore my flamegraph - it's for my local time where we don't have daylight savings. When I change my tz to the pacific one I now see a different picture - it seems there are quite a few things to optimize

is the codegen for GetDatePart() reasonable?

more or less, but we might need to extract it for Year separately since it's on a hot path and inline into Year property.
Also, it's executed from 3 different places in this flamegraph

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Issue Details

---

System.Tests.Perf_DateTime.GetNow has regressed across multiple configurations.

Reporting System:

Looking at the commit diff, #66282 seems to be to blame.

Repro:

git clone https://github.com/dotnet/performance.git
py .\performance\scripts\benchmarks_monthly.py net7.0-preview2 net7.0-preview3 --filter System.Tests.Perf_DateTime.GetNow 

## System.Tests.Perf_DateTime.GetNow

Result	Base	Diff	Ratio	Operating System	Bit	Processor Name
Same	112.05	114.53	0.98	Windows 10	X64	Intel Xeon CPU E5-1650 v4 3.60GHz
Same	93.72	99.81	0.94	Windows 11	X64	AMD Ryzen Threadripper PRO 3945WX 12-Cores
Slower	73.98	83.75	0.88	Windows 11	X64	AMD Ryzen 9 5900X
Same	131.78	149.14	0.88	Windows 11	X64	Intel Core i5-4300U CPU 1.90GHz (Haswell)
Same	118.61	116.32	1.02	Windows 11	X64	Unknown processor
Same	88.62	86.35	1.03	Windows 11	X64	Intel Core i7-8700 CPU 3.20GHz (Coffee Lake)
Same	103.63	99.92	1.04	Windows 11	X64	Intel Core i9-9900T CPU 2.10GHz
Same	372.20	380.11	0.98	alpine 3.13	X64	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Same	66.48	65.91	1.01	centos 7	X64	Intel Xeon CPU E5530 2.40GHz
Slower	416.66	472.23	0.88	debian 11	X64	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Slower	70.55	139.81	0.50	ubuntu 18.04	X64	Intel Xeon CPU E5-1650 v4 3.60GHz
Same	198.80	190.36	1.04	ubuntu 18.04	X64	Intel Core i7-2720QM CPU 2.20GHz (Sandy Bridge)
Same	240.11	241.49	0.99	alpine 3.12	Arm64	Unknown processor
Same	243.79	242.33	1.01	ubuntu 18.04	Arm64	Unknown processor
Slower	169.90	191.41	0.89	Windows 10	Arm64	Microsoft SQ1 3.0 GHz
Slower	169.84	194.79	0.87	Windows 11	Arm64	Microsoft SQ1 3.0 GHz
Same	403.45	402.18	1.00	Windows 10	X86	Intel Xeon CPU E5-1650 v4 3.60GHz
Slower	244.43	272.36	0.90	Windows 11	X86	AMD Ryzen Threadripper PRO 3945WX 12-Cores
Same	669.31	771.68	0.87	Windows 11	X86	Intel Core i7-10510U CPU 1.80GHz
Same	294.33	296.09	0.99	Windows 7 SP1	X86	Intel Core i7-7700 CPU 3.60GHz (Kaby Lake)
Same	766.67	714.33	1.07	ubuntu 18.04	Arm	ARMv7 Processor rev 3 (v7l)
Slower	1358.46	1709.54	0.79	Windows 10	Arm	Microsoft SQ1 3.0 GHz
Slower	94.22	169.26	0.56	macOS Monterey 12.2.1	X64	Intel Core i7-5557U CPU 3.10GHz (Broadwell)
Same	162.60	158.64	1.02	macOS Monterey 12.3.1	X64	Intel Core i7-4870HQ CPU 2.50GHz (Haswell)

Author:	dakersnar
Assignees:	-
Labels:	area-System.Runtime, tenet-performance, untriaged
Milestone:	7.0.0

[EgorBo]

I'll take a look when I have some spare time 🙂