Post by Ryan Castellucci (they/them) <img src="https://takahe.blankpad.net/media/emoji/infosec.exchange/nonbinary_flag.png" class="emoji" alt="Emoji nonbinary_flag">

4d

@fanf I'm going to give it to you for this, it was dnsmasq calling fsync(2) on the dhcp leases file, which happens fairly frequently because I've got about 80 DHCP clients on my home network.

I have resolved it by LD_PRELOADing libeatmydata.

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4d

@ryanc @fanf so, dnsmasq has a single thread (async?) for dns and dhcp requests, and if dhcp are lagging, they block dns?

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4d

@mdione @fanf I didn't dig into the code, but I believe it is single threaded, and fsync is always blocking by design even on an otherwise non-blocking file descriptor.

But. In common configurations, fsync also has to wait on any other writes that were pending on the same filesystem.

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