From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCHv6] x86/xen: allow privcmd hypercalls to be preempted Date: Fri, 20 Feb 2015 13:51:59 +0000 Message-ID: <54E73BFF.8060804@citrix.com> References: <1424359397-14160-1-git-send-email-david.vrabel@citrix.com> <54E6144A.6030704@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YOnzw-0002bh-2z for xen-devel@lists.xenproject.org; Fri, 20 Feb 2015 13:52:04 +0000 In-Reply-To: <54E6144A.6030704@oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Boris Ostrovsky , David Vrabel , xen-devel@lists.xenproject.org List-Id: xen-devel@lists.xenproject.org On 19/02/15 16:50, Boris Ostrovsky wrote: > On 02/19/2015 10:23 AM, David Vrabel wrote: >> Hypercalls submitted by user space tools via the privcmd driver can >> take a long time (potentially many 10s of seconds) if the hypercall >> has many sub-operations. >> >> A fully preemptible kernel may deschedule such as task in any upcall >> called from a hypercall continuation. >> >> However, in a kernel with voluntary or no preemption, hypercall >> continuations in Xen allow event handlers to be run but the task >> issuing the hypercall will not be descheduled until the hypercall is >> complete and the ioctl returns to user space. These long running >> tasks may also trigger the kernel's soft lockup detection. >> >> Add xen_preemptible_hcall_begin() and xen_preemptible_hcall_end() to >> bracket hypercalls that may be preempted. Use these in the privcmd >> driver. >> >> When returning from an upcall, call xen_maybe_preempt_hcall() which >> adds a schedule point if if the current task was within a preemptible >> hypercall. >> >> Since _cond_resched() can move the task to a different CPU, clear and >> set xen_in_preemptible_hcall around the call. >> >> Signed-off-by: David Vrabel > > Reviewed-by: Boris Ostrovsky Thanks. Applied to stable/for-linus-3.20. David