Don't call flush when circling is triggered in VtRenderer

[skyline75489]

Summary of the Pull Request

Don't call flush when circling is triggered in VtRenderer.

References

Currently every time TriggerCircling is called, VtRenderer will force paint the frame and then flush the internal buffer. This is not really necessary because the max drawing frequency for graphic renderers like DxRenderer is limited. This causes an exceptionally bad case for the "1 million yes" benchmark: every time a “y" is printed, a single line if flushed, which is y(lot of spaces)\n. With this fix, VtRenderer will not flush the buffer eagerly and wait for more text. This improves the throughput.

PR Checklist

• Supports [Performance] vtebench tracking issue #10563
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Documentation updated. If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated.
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[skyline75489]

On my PC, the time needed for "1 million yes" dropped from ~8.0s to 6.2s in WT. For conhost it seems to worsen the performance a bit, because there's more pressure in the GDI renderer, which is heavily slowed down by #10528.

OpenConsole.exe trace

Before:

After:

[zadjii-msft]

I'm gonna temporarily block this while I look up in the archives why this is there. This might be secretly load bearing for something like telnet or something silly.

[zadjii-msft]

for my own reference, these are OS commits 900da83ab6934aad8c5d5d9688968ea7e634c563 and 9f89d02bbbce9283ec3a0fd6193e97f27cbcdb13

[skyline75489]

This actually slows down cat big.txt. Need to investigate a bit.

[skyline75489]

Yeah this slows down the catting of large files significantly. For example for a 100MB file the time needed increases from 20s to 30s. I still don’t quite understand the reason.

[skyline75489]

Closing this because it's not good enough and idk how to improve it.