Hi Alan,
> What cheap is VerifyVersionInfoW? The check is done everytime but the
> overhead might be in the noise. Overall it looks good to me.
I wrote a small benchmark to measure the overhead of the version check
(attached below).
On my SurfaceBook 2 running Windows 10 Build 19041, the version check measures
about ~2.2us (micro seconds) on average, when the
version matches.
Elapsed time 2244us. (for 1,000 iterations)
On a Windows 2016 Data Center Server the version check is much smaller ~0.13us
(micro seconds) on average, when the version doesn't
match.
Elapsed time 128us. (for 1,000 iterations)
I think the overhead is reasonably small compared to everything else. Please
let me know if it's acceptable and if we can proceed.
Thanks,
Nikola
Benchmark program:
int main()
{
LARGE_INTEGER start_time, end_time, elapsed_us;
LARGE_INTEGER frequency;
QueryPerformanceFrequency(&frequency);
QueryPerformanceCounter(&start_time);
int count = 0;
for (int i = 0; i < 1000; i++) {
count += IsWindows10RS3OrGreater();
}
QueryPerformanceCounter(&end_time);
elapsed_us.QuadPart = end_time.QuadPart - start_time.QuadPart;
elapsed_us.QuadPart *= 1000000;
elapsed_us.QuadPart /= frequency.QuadPart;
printf("Elapsed time %lldus.\n", elapsed_us.QuadPart);
}
-----Original Message-----
From: Alan Bateman <[email protected]>
Sent: July 31, 2020 1:29 PM
To: Nikola Grcevski <[email protected]>; [email protected]
Subject: Re: RFR(s): Improving performance of Windows socket connect on the
loopback adapter
On 28/07/2020 15:03, Nikola Grcevski wrote:
> Hi Alan,
>
> Thanks again for testing this change. I dug deep into the issue yesterday and
> got some answers from the Windows Networking team.
>
> The issue is that the flag TCP_INITIAL_RTO_NO_SYN_RETRANSMISSIONS, which we
> passed in to completely eliminate the network delay, isn't defined (or
> checked) on Windows 10 versions prior to RS3 (Redstone 3). The flag was
> interpreted as TCP_INITIAL_RTO_DEFAULT_MAX_SYN_RETRANSMISSIONS, causing a
> retry of 255 times, each one taking 500ms. This made each individual connect
> delay take 128 seconds in total.
>
> I was advised to change the code to perform a runtime check on the exact
> Windows version and unless it's Windows 10RS3 or later, we should set the
> retransmissions to 1. Strangely enough, we can't set it to 0, which is a
> special value interpreted as use the default. With retransmission count of 1,
> we speed up the localhost connects on older versions of Windows by factor of
> 2.
>
> I have prepared a new webrev with the runtime check for review here:
> http://cr.openjdk.java.net/~adityam/nikola/fast_connect_loopback_4/
>
> For the Windows version check function I followed the naming standards the
> SDK uses in:
> https://docs.microsoft.com/en-us/windows/win32/api/versionhelpers/
>
> If it's not a suitable function name please let me know. They have added this
> helper function for .NET 4.8 but it's not there yet for Win32. Hopefully, it
> comes provided by Microsoft in a future SDK update and we can remove the
> helper. I attempted to use IsWindowsVersionOrGreater, but unfortunately that
> API doesn't allow me to specify the build number to detect RS3.
>
What cheap is VerifyVersionInfoW? The check is done everytime but the overhead
might be in the noise. Overall it looks good to me.
-Alan
