Hi Benjamin, On Mon, 14 Jul 2025 14:37:33 +0200, Benjamin Berg wrote: > Hi Tiwei, > > this is pretty cool, I really did not expect patches for SMP :-)
I'm really happy you like it. :) > > I have not dived in a lot. From a cursory glance, I expect that there > are currently still issues if a process is actually multi-threaded. But > even this state is really neat already. > > As for proper multi-threading support, I would like to make sure you > are aware of the flush_tlb_* functions in tlbflush.h. These will need > to be updated so that these flushes happen synchronously as another > thread might otherwise access data for too long. > > There are probably a few things to figure out in that regard about > where/when to flush the TLB entries in a multi-threaded userspace. > After all, there can be up to the number of CPUs worker threads and one > probably only wants one of them to sync the TLBs at any point in tmie. That makes sense! Thanks for the heads-up! I'll take a closer look. > > Anyway, nice work! Thanks! :) Tiwei > Benjamin > > On Mon, 2025-07-14 at 01:25 +0800, Tiwei Bie wrote: > > From: Tiwei Bie <tiwei....@antgroup.com> > > > > This is a follow-up to the discussion in this thread: > > https://lore.kernel.org/linux-um/20250711065021.2535362-4-tiwei....@linux.dev/ > > > > Currently, this is still a PoC and requires further improvements. > > > > I performed a kernel build test inside UML with 8 virtual CPUs > > enabled: > > > > $ tar xf linux-6.15.tar.gz > > $ cd linux-6.15 > > $ make ARCH=um defconfig > /dev/null > > $ time make ARCH=um -j16 > /dev/null > > > > real 6m2.529s > > user 43m37.665s > > sys 0m34.585s > > $ ./linux --version > > 6.15.0 > > $ cat /proc/cpuinfo | grep -c '^processor' > > 8 > > > > Here are some steps to try out SMP support in UML: > > > > 1. Build UML with CONFIG_SMP=y and, for example, CONFIG_NR_CPUS=8. > > > > 2. Launch a UML instance with, for example, 8 virtual CPUs. > > > > $ ./linux mem=16G ncpus=8 nohz=n seccomp=on init=/bin/sh \ > > ubd0=$your_rootfs_image > > > > This patchset depends on the following patchset: > > https://lore.kernel.org/linux-um/20250711065021.2535362-1-tiwei....@linux.dev/ > > > > Tiwei Bie (4): > > um: Stop tracking virtual CPUs via mm_cpumask() > > um: Remove unused cpu_data and current_cpu_data macros > > um: vdso: Implement __vdso_getcpu() via syscall > > um: Add SMP support > > > > arch/um/Kconfig | 28 ++- > > arch/um/include/asm/Kbuild | 3 + > > arch/um/include/asm/current.h | 5 +- > > arch/um/include/asm/hardirq.h | 24 ++- > > arch/um/include/asm/irqflags.h | 4 +- > > arch/um/include/asm/mmu.h | 7 + > > arch/um/include/asm/mmu_context.h | 11 -- > > arch/um/include/asm/pgtable.h | 2 + > > arch/um/include/asm/processor-generic.h | 8 +- > > arch/um/include/asm/smp.h | 31 +++- > > arch/um/include/asm/spinlock.h | 8 + > > arch/um/include/linux/smp-internal.h | 8 + > > arch/um/include/linux/time-internal.h | 3 + > > arch/um/include/shared/kern_util.h | 2 + > > arch/um/include/shared/longjmp.h | 3 +- > > arch/um/include/shared/os.h | 12 +- > > arch/um/include/shared/smp.h | 14 ++ > > arch/um/kernel/Makefile | 1 + > > arch/um/kernel/irq.c | 31 +++- > > arch/um/kernel/ksyms.c | 2 +- > > arch/um/kernel/mem.c | 2 + > > arch/um/kernel/process.c | 19 +- > > arch/um/kernel/skas/mmu.c | 16 +- > > arch/um/kernel/smp.c | 223 > > ++++++++++++++++++++++++ > > arch/um/kernel/time.c | 48 +++-- > > arch/um/kernel/tlb.c | 5 +- > > arch/um/kernel/trap.c | 2 +- > > arch/um/kernel/um_arch.c | 60 ++++++- > > arch/um/os-Linux/Makefile | 4 +- > > arch/um/os-Linux/file.c | 72 ++++++-- > > arch/um/os-Linux/main.c | 5 +- > > arch/um/os-Linux/process.c | 15 ++ > > arch/um/os-Linux/signal.c | 16 +- > > arch/um/os-Linux/skas/process.c | 1 + > > arch/um/os-Linux/smp.c | 44 +++++ > > arch/um/os-Linux/start_up.c | 3 + > > arch/um/os-Linux/time.c | 29 +-- > > arch/um/os-Linux/user_syms.c | 5 + > > arch/x86/um/vdso/um_vdso.c | 18 +- > > 39 files changed, 695 insertions(+), 99 deletions(-) > > create mode 100644 arch/um/include/asm/spinlock.h > > create mode 100644 arch/um/include/linux/smp-internal.h > > create mode 100644 arch/um/include/shared/smp.h > > create mode 100644 arch/um/kernel/smp.c > > create mode 100644 arch/um/os-Linux/smp.c > > >
