- FPU context is stored only if conflict between 2 FPU users or while
exporting context of a process to userspace while it is the active
user of FPU
- FPU has its owner (fpu_owner) which points to the process whose
state is currently loaded in FPU
- the FPU exception is only turned on when scheduling a process which
is not the owner of FPU
- FPU state is restored for the process that generated the FPU
exception. This process runs immediately without letting scheduler
to pick a new process to resolve the FPU conflict asap, to minimize
the FPU thrashing and FPU exception hadler execution
- faster all non-FPU-exception kernel entries as FPU state is not
checked nor saved
- removed MF_USED_FPU flag, only MF_FPU_INITIALIZED remains to signal
that a process has used FPU in the past
- A staging directory is always used to avoid oversized images;
- As a consequence, the zero-filling is removed so no more "out of
space" errors should be printed to the console;
- The root and usr partition sizes are computed so less space should be
wasted (the root partition gets extra 1MB zones and 64 inodes for
run-time though and hardlinks/holes make the used space slightly less
than expected); USRMB (and the new ROOTMB) are now used to enforce
a minimum size rather than set the size;
- TMPDISK1-3 are renamed to more meaningful names (and TMPDISK2 is
dropped because a separate tmp directory is no longer needed);
- The ramdisks are truncated at the end to save memory (not sure
whether it is actually released though).
There seems to have been a broken assumption in the fpu context
restoring code. It restores the context of the running process, without
guarantee that the current process is the one that will be scheduled.
This caused fpu saving for a different process to be triggered without
fpu hardware being enabled, causing an fpu exception in the kernel. This
practically only shows up with DEBUG_RACE on. Fix my thruby+me.
The fix
. is to only set the fpu-in-use-by-this-process flag in the
exception handler, and then take care of fpu restoring when
actually returning to userspace
And the patch
. translates fpu saving and restoring to c in arch_system.c,
getting rid of a juicy chunk of assembly
. makes osfxsr_feature private to arch_system.c
. removes most of the arch dependent code from do_sigsend
