On Friday, 14 June 2024 20:53:04 BST Walter Dnes wrote: > On Fri, Jun 14, 2024 at 11:54:52AM +0100, Michael wrote > > > I would think 46-48°C is refreshingly cool, but it very much depends > > on the CPU chip, the MoBo and its BIOS/microcode settings. > > I looked up my CPU (see my reply to Dale). The max temp allowed is > 71.3 C. A short kernel compile is one thing. I tried schedutil during > an emerge world update, and the temp was hitting 70 C. Ouch! schedutil > has to go.
Not so fast! :-) The maximum temperature at which your CPU die with its 65W TDP starts throttling to keep its temperatures safe is 100°C TjMax. Look at the TJunction number here: https://www.intel.com/content/www/us/en/products/sku/199271/intel-core-i510400-processor-12m-cache-up-to-4-30-ghz/specifications.html As I understand it 72°C is the TCase temperature. sys-apps/lm-sensors are meant to report TjMax, the core temperature of the CPU. The TCase can be measured (approximately) with an infrared thermometer, or by hacking the cover of the CPU (seriously NOT recommended!). Assuming you have enough RAM and you use all your CPU threads, a big package compile (e.g. chromium) will indicate typical max temperatures your particular installation achieves. Something like MAKEOPTS="-j13 -l12.8" ought to squeeze the juice out of it. The TjMax is controlled by the MoBo firmware and any updates to it. Aftermarket CPU coolers and thermal paste will give you an edge here over stock options for desktops, especially when ambient temperatures hit higher numbers in the summer months. For a laptop there are limited things to try, e.g. better thermal pads/paste and a cooling pad with external fans. However, such measures may only be necessary if the stock cooler does not keep temperatures within normal operating range. According to Intel anything below 100°C is 'normal'. If this were my CPU I would not worry with temperatures ~70-85°C. Above that I would install a better CPU cooler. > > I recall an early i7 CPU laptop would not go above 2,400MHz when > > 4core/8threads were running, but on single core processes I would > > see it on i7z jumping up to 4,200MHz. > > Speaking of cores+threads... I had always thought my cpu had 12 > cores. i.e. /proc/cpuinfo showed 12 "cpus" as did directory > /sys/devices/system/cpu/ But I was wrong. The specs show 6 real cores, > plus hyperthreading. You can use lscpu. It shows threads and cores. > See Greg Kroah-Hartman's presentation about the > security issue called "hyperthreading"... > https://events19.linuxfoundation.org/wp-content/uploads/2018/07/gregkh_mds.p > df Read it and weep. Page 6 summarizes it succinctly... > > ================================================== > OpenBSD was right > * Guessed more problems would be in this area > * Disabled SMT for Intel chips in June 2018 > * Repeated the plea to disable this in August 2018 > * Prevented almost all MDS issues automatically > * Security over performance > * Huge respect! > ================================================== > > I immediately went into the BIOS and disabled hyperthreading... and > adjusted makeopts in make.conf <G> In June 2018 and for 2019 the idea to disable hyperthreading would be a security precaution, especially for datacenters and systems running VM installations. I am not sure this is either necessary or even recommended anymore. More knowledgeable contributors should chime in here. As far as I know, OEM MoBo firmware updates, CPU microcode releases, OS kernels, compilers and applications have implemented a lot of fixes and patches to cover the litany of CPU bugs and vulnerabilities discovered since then. If you run lscpu and also check your dmesg output, you'll see what known vulnerabilities your CPU may be still be exposed to - if any. Sadly Intel are not very charitable toward their older retail market CPUs and did not release needed microcode updates. This steered me away from their CPUs since then. You could also take a look at the spectre-meltdown-checker if you want a more detailed report on the latest revealed vulnerabilities: https://github.com/speed47/spectre-meltdown-checker
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