如何在4.0环境中加速Powershell的启动？

Question

I'm considering using Powershell scripts for triggers on our Perforce server. Unfortunately, even on our fast hardware it still takes 2 seconds for Powershell to start up. Now, this doesn't seem like much time unless you consider that 200 users are pounding the server constantly, and a trigger may (depending on conditions) cause a table lock while it runs, stalling out other related requests.

I'm looking for ways to reduce the startup time of Powershell. Things that I've found on Google:

• Reduce the profile. This is a default installation, no profile customization, no PSCX, etc. so this doesn't help.
• Run NGEN on Posh binaries. This is old advice for a V1 issue. We're on V2.
• Keep it warm. Initial Posh startup is slow but later startups are fast. Also not helpful for us. On the server the warm start is 2 seconds and it's kept warm by frequent requests.
• Don't use Powershell for this purpose. Well, I'm hoping to avoid that "solution"...

Does anyone have any other suggestions for cutting startup time? I'm not expecting a startup as fast as cmd.exe or a .NET command line app, but if I can get this to .5 seconds I think we'll be ok. Impossible?

UPDATE - it turns out this is a 4.0 issue. If I add a config file as described in another SO question the startup takes 2 seconds. If I leave it at its default, then startup is under a quarter second.

Then I thought..perhaps it's a 4.0 GAC issue. So I ran the script on the PowerShell Blog but it says all the assemblies are already ngen'd. I made sure that it is indeed using the 4.0 ngen as well.

So I'm left with two options:

• Figure out why 4.0 is so much more expensive than 3.5.
• Switch to the 3.5 framework where I do not need it and I do need the performance.

I'd love to solve the first but don't know where to start. Can anyone help?

Answer 1

Run NGEN on Posh binaries. This is old advice for a V1 issue. We're on V2.

I've been playing with this under V3, and I found out that some images were generated.

And it certainly feels like startup is now much faster. I'll know better after a reboot, as the first time is always the worst. The (my updated) script to do so with Win 7 is

$env:path = [Runtime.InteropServices.RuntimeEnvironment]::GetRuntimeDirectory()
[AppDomain]::CurrentDomain.GetAssemblies() | % {
  if (! $_.location) {continue}
  $Name = Split-Path $_.location -leaf
  Write-Host -ForegroundColor Yellow "NGENing : $Name"
  ngen install $_.location | % {"`t$_"}
}

Answer 2

Following an excellent answer to my question on Technet , I discovered a much easier way to trigger NGEN manually (since it seems it doesn't happen automatically on a clean install of Windows 8.1):

schtasks /Run /TN "\Microsoft\Windows\.NET Framework\.NET Framework NGEN v4.0.30319"
schtasks /Run /TN "\Microsoft\Windows\.NET Framework\.NET Framework NGEN v4.0.30319 64"

Answer 3

I'm afraid you're probably out of luck if you stick with the console host powershell.exe, unless you feel like writing an optimized script processor by hosting a runspace/runspacefactory in a custom console application - or a windows service - you roll yourself. You might shave a second off, but 0.5s startup for a .NET application is unlikely, especially if the servers are tight for memory.