Long time postgres developer, working at Microsoft.
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npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j
Profile Code
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npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j Show more details
Published at
2023-11-21T05:06:31+01:00 Event JSON
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Last Notes npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1hxa…j94a They either train as pcie 4, don't work at all, or also have AER errors. So I suspect it's a mainboard / firmware issue :/ npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1h59…waea Thanks. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1h59…waea Several DEs start themselves via systemd these days, so a graphical terminal will often have the systemd limits applied. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1h59…waea (since most things spawn from somewhere within a systemd instance these days, the pam limits are quickly overriden by systemd) npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Here are the slides for a talk I just gave about using perf c2c to find cache line contention in postgres: npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1hxa…j94a Yep. This is with turbo verified to be disabled, C-states disabled and frequency monitored... npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec A potentially interesting detail: If I interpret https://community.intel.com/t5/Software-Tuning-Performance/Understanding-PCICFG-space-information/m-p/1138821#M6581 correctly, both my CPUs are 18 core models with some cores disabled. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1yc6…lmgn Nope. No difference above noise. That core is the only "really slow" one. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec I don't think that's it - I added userspace vs kernel cycles,instructions: npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec My best theory so far is that somehow on that one core there are more conflicts on L1i entries, leader to a lower hit rate. I haven't figured out what the precise keying scheme for the L1i is (it's 8 way associative). npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub142j…7ugm Yep. There are practically no interrupts, there are no SMIs, no evidence of throttling in performance counters. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1e5z…g25u It's possible, but somehow it seems odd to end up with different numbers of L1i misses etc, without causing apparent corruption. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1e5z…g25u The others perform like 11, 10 is slow. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1e5z…g25u Core 10 is the the first core of the second socket, 11 the second. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub17lg…9uux Hah. This is weird, but not that kind of weird, I strongly suspect. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub16hg…mtal It's the same numa node... npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec https://gist.github.com/anarazel/ca7d1db68fb7380d21f6fd819a147df1 npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Well, color me very confused. In a CPU bound workload two cores on the same socket have substantially different performance (32% slowdown). If I just migrate the running process between the cores, performance changes immediately. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub16ew…us82 I assume this one is also mounted with barrier=0? npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1hxa…j94a Very interesting. Thanks. A depressingly large performance diff between ext4 and btrfs, even with nocow. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub12yj…3l94 Thanks. What filesystem is this? npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1jpa…6p97 I'm curious about your results with the SK Hynic, because they're the first non-samsung one where FUA writes are slower. Albeit at a much lower degree. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1jpa…6p97 Thanks! npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Collecting the information here: npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1u8f…p9n0 Thanks! npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub1p4g…8pte Thanks! npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Going to collect the information here: npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Any chance a few folks could run the following fio command on various SSDs and tell me the latency, drive model and filesystem? npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec The "new" linux CVE approach seems ... unhelpful at best. I know from experience that dealing with security reports is a pain and I assume that's way worse for linux than for Postgres. But this just seems to purely be aimed at annoying everyone. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec Congratulations to fellow postgres hackers @npub1zcv…cczq and Richard Guo for becoming committers! npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec I did not think that finding a security vulnerability would lead to tabloids digging around my life. Including "analyzing" (aka making things up) the one personal-ish picture I've ever shared on social media. FFS. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub17lg…9uux FWIW, I hadn't been on twitter in months, and this made me go back - at least earlier on there was distinct information, particularly around reverse engineering efforts. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec I am a bit concerned by all the focus on small-ish projects with overwhelmed maintainers. There indeed are a lot of problems in that area. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec @npub178r…qekt Even if you don't care about collateral harm, with something like a backdoor in ssh, it just seem too likely you'd otherwise accidentally make yourself vulnerable too, somewhere in your org. npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec I wholeheartedly agree with what Russ wrote here: npub1ly44p7gfxnqm237hpxc8dynusdz4jfvtqrh5nmgrwcrsxkmz5n6q6gks2j AndresFreundTec I accidentally found a security issue while benchmarking postgres changes.
