Pcap networking kills performance?

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scubasteve
Posts: 1
Joined: Sun 14 Jul, 2019 10:27 pm

Pcap networking kills performance?

Post by scubasteve »

I've been on a retro binge lately and absolutely loving PCEm. Ran into an issue the other day though that almost made me give up on it, so I wanted to post here (first time) to make sure you're aware.

Thing is, I was seeing performance dips like crazy trying to emulate anything above a Pentium 75 on my i7 Skylake. And I do realize that being the actual limit of what I can emulate wasn't out of the question (hence almost giving up.) I started fiddling with settings though and eventually found that switching from pcap to slirp completely resolved the issue, and I am now able to run a 233 Mmx at almost constant 100%.

The really weird thing is this was happening not only in Windows 95, but also in DOS where I don't think any kind of network discovery stuff would be running. It seemed to impact performance equally on both DOS and Windows.
xpclient
Posts: 7
Joined: Thu 15 Apr, 2021 4:43 pm

Re: Pcap networking kills performance?

Post by xpclient »

Yes I can confirm there is a performance hit by switching PCem v17 from SLiRP to Pcap. On my 6 core gaming laptop CPU, Core i7 9750H, all versions of Windows 9x can emulate a Pentium MMX 166 smoothly. They run extremely smoothly - Windows 95, 98 and Me. SLiRP gives internet connectivity but not local network of course as is very well known. As soon as I switch to Pcap, the emulator begins to hang and stutter. It can't even play the startup sound smoothly. Shutting down takes 3 minutes. The "It is now safe to turn off" screen appeared a full 90 seconds after "Please wait while Windows shuts down" once Pcap was enabled.

Reduced the CPU to Pentium 75. Then the sounds play smoothly again with Pcap on.

With SLiRP, no issues. :) Thanks to this dev for this fantastic emulator anyway.
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