Re: [RFC][PATCH v2 5/5] sched: User Mode Concurency Groups
From: Mark Rutland <mark.rutland@arm.com>
Date: 2022-01-21 16:58:48
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linux-mm, lkml
On Thu, Jan 20, 2022 at 04:55:22PM +0100, Peter Zijlstra wrote:
User Managed Concurrency Groups is an M:N threading toolkit that allows constructing user space schedulers designed to efficiently manage heterogeneous in-process workloads while maintaining high CPU utilization (95%+). XXX moar changelog explaining how this is moar awesome than traditional user-space threading.
Awaiting a commit message that I can parse, I'm just looking at the entry bits for now. TBH I have no idea what this is actually trying to do... [...]
quoted hunk ↗ jump to hunk
--- a/include/linux/entry-common.h +++ b/include/linux/entry-common.h@@ -23,6 +23,10 @@ # define _TIF_UPROBE (0) #endif +#ifndef _TIF_UMCG +# define _TIF_UMCG (0) +#endif + /* * SYSCALL_WORK flags handled in syscall_enter_from_user_mode() */@@ -43,11 +47,13 @@ SYSCALL_WORK_SYSCALL_EMU | \ SYSCALL_WORK_SYSCALL_AUDIT | \ SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ + SYSCALL_WORK_SYSCALL_UMCG | \ ARCH_SYSCALL_WORK_ENTER) #define SYSCALL_WORK_EXIT (SYSCALL_WORK_SYSCALL_TRACEPOINT | \ SYSCALL_WORK_SYSCALL_TRACE | \ SYSCALL_WORK_SYSCALL_AUDIT | \ SYSCALL_WORK_SYSCALL_USER_DISPATCH | \ + SYSCALL_WORK_SYSCALL_UMCG | \ SYSCALL_WORK_SYSCALL_EXIT_TRAP | \ ARCH_SYSCALL_WORK_EXIT)@@ -221,8 +227,11 @@ static inline void local_irq_disable_exi */ static inline void irqentry_irq_enable(struct pt_regs *regs) { - if (!regs_irqs_disabled(regs)) + if (!regs_irqs_disabled(regs)) { local_irq_enable(); + if (user_mode(regs) && (current->flags & PF_UMCG_WORKER)) + umcg_sys_enter(regs, -1); + } }
Perhaps it would make sense to have separate umcg_sys_enter(regs) and umcg_sys_enter_syscall(regs, syscallno)? Even if the former is just a wrapper, to make the entry/exit bits clearly correspond for all the !syscall cases? Also, is the syscall case meant to nest within this, or syscall entry paths not supposed to call irqentry_irq_enable() ?
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/**@@ -232,8 +241,11 @@ static inline void irqentry_irq_enable(s */ static inline void irqentry_irq_disable(struct pt_regs *regs) { - if (!regs_irqs_disabled(regs)) + if (!regs_irqs_disabled(regs)) { + if (user_mode(regs) && (current->flags & PF_UMCG_WORKER)) + umcg_sys_exit(regs); local_irq_disable(); + } }
Do the umcg_sys_{enter,exit}() calls need to happen with IRQs unmasked?
* If not (and this nests): for arm64 these can live in our
enter_from_user_mode() and exit_to_user_mode() helpers.
* If so (or this doesn't nest): for arm64 we'd need to rework our
local_daif_{inherit,restore,mask}() calls to handle this, though I've been
meaning to do that anyway to handle pseudo-NMI better.
Either way, it looks like we'd need helpers along the lines of:
| static __always_inline void umcg_enter_from_user(struct pt_regs *regs)
| {
| if (current->flags & PF_UMCG_WORKER)
| umcg_sys_enter(regs, -1);
| }
|
| static __always_inline void umcg_exit_to_user(struct pt_regs *regs)
| {
| if (current->flags & PF_UMCG_WORKER)
| umcg_sys_exit(regs);
| }
Thanks,
Mark.