Add warning for suspected slow system clocksource setting (#10636)
This PR does 2 main things: 1) Add warning for suspected slow system clocksource setting. This is Linux specific. 2) Add a `--check-system` argument to redis which runs all system checks and prints a report. ## System checks Add a command line option `--check-system` which runs all known system checks and provides a report to stdout of which systems checks have failed with details on how to reconfigure the system for optimized redis performance. The `--system-check` mode exists with an appropriate error code after running all the checks. ## Slow clocksource details We check the system's clocksource performance by running `clock_gettime()` in a loop and then checking how much time was spent in a system call (via `getrusage()`). If we spend more than 10% of the time in the kernel then we print a warning. I verified that using the slow clock sources: `acpi_pm` (~90% in the kernel on my laptop) and `xen` (~30% in the kernel on an ec2 `m4.large`) we get this warning. The check runs 5 system ticks so we can detect time spent in kernel at 20% jumps (0%,20%,40%...). Anything more accurate will require the test to run longer. Typically 5 ticks are 50ms. This means running the test on startup will delay startup by 50ms. To avoid this we make sure the test is only executed in the `--check-system` mode. For a quick startup check, we specifically warn if the we see the system is using the `xen` clocksource which we know has bad performance and isn't recommended (at least on ec2). In such a case the user should manually rung redis with `--check-system` to force the slower clocksource test described above. ## Other changes in the PR * All the system checks are now implemented as functions in _syscheck.c_. They are implemented using a standard interface (see details in _syscheck.c_). To do this I moved the checking functions `linuxOvercommitMemoryValue()`, `THPIsEnabled()`, `linuxMadvFreeForkBugCheck()` out of _server.c_ and _latency.c_ and into the new _syscheck.c_. When moving these functions I made sure they don't depend on other functionality provided in _server.c_ and made them use a standard "check functions" interface. Specifically: * I removed all logging out of `linuxMadvFreeForkBugCheck()`. In case there's some unexpected error during the check aborts as before, but without any logging. It returns an error code 0 meaning the check didn't not complete. * All these functions now return 1 on success, -1 on failure, 0 in case the check itself cannot be completed. * The `linuxMadvFreeForkBugCheck()` function now internally calls `exit()` and not `exitFromChild()` because the latter is only available in _server.c_ and I wanted to remove that dependency. This isn't an because we don't need to worry about the child process created by the test doing anything related to the rdb/aof files which is why `exitFromChild()` was created. * This also fixes parsing of other /proc/\<pid\>/stat fields to correctly handle spaces in the process name and be more robust in general. Not that before this fix the rss info in `INFO memory` was corrupt in case of spaces in the process name. To recreate just rename `redis-server` to `redis server`, start it, and run `INFO memory`.
src/syscheck.c
0 → 100644
src/syscheck.h
0 → 100644
Please register or sign in to comment