Lagspike saga

Announcements about major changes in Haven & Hearth.

Re: Lagspike saga

Postby loftar » Mon Mar 04, 2019 12:44 pm

Granger wrote:flash_vol_create in /sys/fs/bcache/<cset-uuid> could, according to bcache documentation, be a way to emulate overprovision ex post facto.

Not sure what you mean by that. I don't obviously see what that would have with the Flash provisioning to do.

Granger wrote:Thinking a bit further about online TRIM on the backed filesystem: could also be an answer, as it would tell bcache which blocks got free'd. Without it bcache might see the cache running full and doing a purge of multiple erase blocks all over the cache, the latencies of a bunch of small discards in parallel might add up to the stalls you see... Depends on the discard setting in /sys/block/<cdev>/bcache though.

I would assume that bcache is fundamentally tuned to run with the cache constantly full. Though, just remounting the filesystem with discard support should be an easy enough test that doesn't take any downtime, so I guess there's no reason to not test.
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Re: Lagspike saga

Postby Granger » Mon Mar 04, 2019 1:25 pm

loftar wrote:
Granger wrote:flash_vol_create in /sys/fs/bcache/<cset-uuid> could, according to bcache documentation, be a way to emulate overprovision ex post facto.

Not sure what you mean by that. I don't obviously see what that would have with the Flash provisioning to do.

From the documentation:
flash_vol_create
Echoing a size to this file (in human readable units, k/M/G) creates a thinly
provisioned volume backed by the cache set.

I read this a it being possible to create a block device that is backed by the cache devices. Writing zero blocks to that should turn it from being thinly provisioned from the bcache perspective into being allocated (reducing their capacity for caching) but should (given what is speculated about the inner workings SSDs these days, fully zero'd blocks being treated as being TRIM'd) free these blocks from the SSD controller perspective, thus should be a way to generate overprovisioning without having to destroy the cache.

The other (possibly more clean) option would be do disable writeback and then remove the cache device, recreate with a reduced partition size after a secure erase of the SSDs and re-add them (bcache cookbook example F).
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Re: Lagspike saga

Postby loftar » Mon Mar 04, 2019 1:43 pm

Granger wrote:fully zero'd blocks being treated as being TRIM'd

I was not aware of that speculated mechanism. Might be worth trying, then.

Granger wrote:The other (possibly more clean) option would be do disable writeback and then remove the cache device, recreate with a reduced partition size after a secure erase of the SSDs and re-add them (bcache cookbook example F).

Indeed, that would be the obvious thing to try, but that's also what I meant be requiring a bit of downtime to rebuild a new RAID device and such (flushing the bcache probably also takes a wee bit of time). If I can't think of anything better, that's probably what I'll end up trying.
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Re: Lagspike saga

Postby Reyajh » Thu Mar 07, 2019 12:38 am

...umm, not to interrupt anything important going on but, could we possibly get a running in place emote, please? :roll:
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Re: Lagspike saga

Postby Granger » Sat Mar 09, 2019 9:35 pm

48h later and I either have acclimated myself so I don't notice the lags anymore... or they're gone.

Which is it?
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Re: Lagspike saga

Postby Robertzon » Sat Mar 09, 2019 9:54 pm

I haven't lagged out for a while as well now, perhaps one lag spike in 4 hours of playtime
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Re: Lagspike saga

Postby The_Blode » Sun Mar 10, 2019 3:11 am

I've been assuming they've been happening while mining or harvesting, but it's been a while since i've seen one while actively playing
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Re: Lagspike saga

Postby Grog » Sun Mar 10, 2019 11:34 pm

getting hard lag spikes again
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Re: Lagspike saga

Postby trinh » Tue Mar 12, 2019 8:43 pm

something is going on right now? I'm getting pretty high lag spikes since 3-4h
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Re: Lagspike saga

Postby Forik » Tue Mar 12, 2019 8:47 pm

It's lagspiking pretty heavily since the update
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