From: Thomas Gleixner <tglx@linutronix.de>
To: Sohil Mehta <sohil.mehta@intel.com>, x86@kernel.org
Cc: Sohil Mehta <sohil.mehta@intel.com>,
Tony Luck <tony.luck@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>, Jens Axboe <axboe@kernel.dk>,
Christian Brauner <christian@brauner.io>,
Peter Zijlstra <peterz@infradead.org>,
Shuah Khan <shuah@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Jonathan Corbet <corbet@lwn.net>, Ashok Raj <ashok.raj@intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Gayatri Kammela <gayatri.kammela@intel.com>,
Zeng Guang <guang.zeng@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Randy E Witt <randy.e.witt@intel.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
Ramesh Thomas <ramesh.thomas@intel.com>,
linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall
Date: Fri, 24 Sep 2021 13:04:25 +0200 [thread overview]
Message-ID: <87r1dedykm.ffs@tglx> (raw)
In-Reply-To: <20210913200132.3396598-12-sohil.mehta@intel.com>
On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> Add a new system call to allow applications to block in the kernel and
> wait for user interrupts.
>
> <The current implementation doesn't support waking up from other
> blocking system calls like sleep(), read(), epoll(), etc.
>
> uintr_wait() is a placeholder syscall while we decide on that
> behaviour.>
>
> When the application makes this syscall the notification vector is
> switched to a new kernel vector. Any new SENDUIPI will invoke the kernel
> interrupt which is then used to wake up the process.
>
> Currently, the task wait list is global one. To make the implementation
> scalable there is a need to move to a distributed per-cpu wait list.
How are per cpu wait lists going to solve the problem?
> +
> +/*
> + * Handler for UINTR_KERNEL_VECTOR.
> + */
> +DEFINE_IDTENTRY_SYSVEC(sysvec_uintr_kernel_notification)
> +{
> + /* TODO: Add entry-exit tracepoints */
> + ack_APIC_irq();
> + inc_irq_stat(uintr_kernel_notifications);
> +
> + uintr_wake_up_process();
So this interrupt happens for any of those notifications. How are they
differentiated?
>
> +int uintr_receiver_wait(void)
> +{
> + struct uintr_upid_ctx *upid_ctx;
> + unsigned long flags;
> +
> + if (!is_uintr_receiver(current))
> + return -EOPNOTSUPP;
> +
> + upid_ctx = current->thread.ui_recv->upid_ctx;
> + upid_ctx->upid->nc.nv = UINTR_KERNEL_VECTOR;
> + upid_ctx->waiting = true;
> + spin_lock_irqsave(&uintr_wait_lock, flags);
> + list_add(&upid_ctx->node, &uintr_wait_list);
> + spin_unlock_irqrestore(&uintr_wait_lock, flags);
> +
> + set_current_state(TASK_INTERRUPTIBLE);
Because we have not enough properly implemented wait primitives you need
to open code one which is blantantly wrong vs. a concurrent wake up?
> + schedule();
How is that correct vs. a spurious wakeup? What takes care that the
entry is removed from the list?
Again. We have proper wait primitives.
> + return -EINTR;
> +}
> +
> +/*
> + * Runs in interrupt context.
> + * Scan through all UPIDs to check if any interrupt is on going.
> + */
> +void uintr_wake_up_process(void)
> +{
> + struct uintr_upid_ctx *upid_ctx, *tmp;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&uintr_wait_lock, flags);
> + list_for_each_entry_safe(upid_ctx, tmp, &uintr_wait_list, node) {
> + if (test_bit(UPID_ON, (unsigned long*)&upid_ctx->upid->nc.status)) {
> + set_bit(UPID_SN, (unsigned long *)&upid_ctx->upid->nc.status);
> + upid_ctx->upid->nc.nv = UINTR_NOTIFICATION_VECTOR;
> + upid_ctx->waiting = false;
> + wake_up_process(upid_ctx->task);
> + list_del(&upid_ctx->node);
So any of these notification interrupts does a global mass wake up? How
does that make sense?
> + }
> + }
> + spin_unlock_irqrestore(&uintr_wait_lock, flags);
> +}
> +
> +/* Called when task is unregistering/exiting */
> +static void uintr_remove_task_wait(struct task_struct *task)
> +{
> + struct uintr_upid_ctx *upid_ctx, *tmp;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&uintr_wait_lock, flags);
> + list_for_each_entry_safe(upid_ctx, tmp, &uintr_wait_list, node) {
> + if (upid_ctx->task == task) {
> + pr_debug("wait: Removing task %d from wait\n",
> + upid_ctx->task->pid);
> + upid_ctx->upid->nc.nv = UINTR_NOTIFICATION_VECTOR;
> + upid_ctx->waiting = false;
> + list_del(&upid_ctx->node);
> + }
What? You have to do a global list walk to find the entry which you
added yourself?
Thanks,
tglx
next prev parent reply other threads:[~2021-09-24 11:04 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 20:01 [RFC PATCH 00/13] x86 User Interrupts support Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 01/13] x86/uintr/man-page: Include man pages draft for reference Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 02/13] Documentation/x86: Add documentation for User Interrupts Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 03/13] x86/cpu: Enumerate User Interrupts support Sohil Mehta
2021-09-23 22:24 ` Thomas Gleixner
2021-09-24 19:59 ` Sohil Mehta
2021-09-27 20:42 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state Sohil Mehta
2021-09-23 22:34 ` Thomas Gleixner
2021-09-27 22:25 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 05/13] x86/irq: Reserve a user IPI notification vector Sohil Mehta
2021-09-23 23:07 ` Thomas Gleixner
2021-09-25 13:30 ` Thomas Gleixner
2021-09-26 12:39 ` Thomas Gleixner
2021-09-27 19:07 ` Sohil Mehta
2021-09-28 8:11 ` Thomas Gleixner
2021-09-27 19:26 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 06/13] x86/uintr: Introduce uintr receiver syscalls Sohil Mehta
2021-09-23 12:26 ` Greg KH
2021-09-24 0:05 ` Thomas Gleixner
2021-09-27 23:20 ` Sohil Mehta
2021-09-28 4:39 ` Greg KH
2021-09-28 16:47 ` Sohil Mehta
2021-09-23 23:52 ` Thomas Gleixner
2021-09-27 23:57 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 07/13] x86/process/64: Add uintr task context switch support Sohil Mehta
2021-09-24 0:41 ` Thomas Gleixner
2021-09-28 0:30 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 08/13] x86/process/64: Clean up uintr task fork and exit paths Sohil Mehta
2021-09-24 1:02 ` Thomas Gleixner
2021-09-28 1:23 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 09/13] x86/uintr: Introduce vector registration and uintr_fd syscall Sohil Mehta
2021-09-24 10:33 ` Thomas Gleixner
2021-09-28 20:40 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 10/13] x86/uintr: Introduce user IPI sender syscalls Sohil Mehta
2021-09-23 12:28 ` Greg KH
2021-09-28 18:01 ` Sohil Mehta
2021-09-29 7:04 ` Greg KH
2021-09-29 14:27 ` Sohil Mehta
2021-09-24 10:54 ` Thomas Gleixner
2021-09-13 20:01 ` [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall Sohil Mehta
2021-09-24 11:04 ` Thomas Gleixner [this message]
2021-09-25 12:08 ` Thomas Gleixner
2021-09-28 23:13 ` Sohil Mehta
2021-09-28 23:08 ` Sohil Mehta
2021-09-26 14:41 ` Thomas Gleixner
2021-09-29 1:09 ` Sohil Mehta
2021-09-29 3:30 ` Andy Lutomirski
2021-09-29 4:56 ` Sohil Mehta
2021-09-30 18:08 ` Andy Lutomirski
2021-09-30 19:29 ` Thomas Gleixner
2021-09-30 22:01 ` Andy Lutomirski
2021-10-01 0:01 ` Thomas Gleixner
2021-10-01 4:41 ` Andy Lutomirski
2021-10-01 9:56 ` Thomas Gleixner
2021-10-01 15:13 ` Andy Lutomirski
2021-10-01 18:04 ` Sohil Mehta
2021-10-01 21:29 ` Thomas Gleixner
2021-10-01 23:00 ` Sohil Mehta
2021-10-01 23:04 ` Andy Lutomirski
2021-09-13 20:01 ` [RFC PATCH 12/13] x86/uintr: Wire up the user interrupt syscalls Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 13/13] selftests/x86: Add basic tests for User IPI Sohil Mehta
2021-09-13 20:27 ` [RFC PATCH 00/13] x86 User Interrupts support Dave Hansen
2021-09-14 19:03 ` Mehta, Sohil
2021-09-23 12:19 ` Greg KH
2021-09-23 14:09 ` Greg KH
2021-09-23 14:46 ` Dave Hansen
2021-09-23 15:07 ` Greg KH
2021-09-23 23:24 ` Sohil Mehta
2021-09-23 23:09 ` Sohil Mehta
2021-09-24 0:17 ` Sohil Mehta
2021-09-23 14:39 ` Jens Axboe
2021-09-29 4:31 ` Andy Lutomirski
2021-09-30 16:30 ` Stefan Hajnoczi
2021-09-30 17:24 ` Sohil Mehta
2021-09-30 17:26 ` Andy Lutomirski
2021-10-01 16:35 ` Stefan Hajnoczi
2021-10-01 16:41 ` Richard Henderson
2021-09-30 16:26 ` Stefan Hajnoczi
2021-10-01 0:40 ` Sohil Mehta
2021-10-01 8:19 ` Pavel Machek
2021-11-18 22:19 ` Sohil Mehta
2021-11-16 3:49 ` Prakash Sangappa
2021-11-18 21:44 ` Sohil Mehta
2021-12-22 16:17 ` Chrisma Pakha
2022-01-07 2:08 ` Sohil Mehta
2022-01-17 1:14 ` Chrisma Pakha
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