| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Tue, 25 Nov 2014 13:57:37 -0500 From: Rik van Riel <riel@...hat.com> To: Marcelo Tosatti <mtosatti@...hat.com>, linux-kernel@...r.kernel.org CC: Luiz Capitulino <lcapitulino@...hat.com>, Steven Rostedt <srostedt@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, kvm@...r.kernel.org Subject: Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq On 11/25/2014 12:21 PM, Marcelo Tosatti wrote: > The problem: > > On -RT, an emulated LAPIC timer instances has the following path: > > 1) hard interrupt > 2) ksoftirqd is scheduled > 3) ksoftirqd wakes up vcpu thread > 4) vcpu thread is scheduled > > This extra context switch introduces unnecessary latency in the > LAPIC path for a KVM guest. > > The solution: > > Allow waking up vcpu thread from hardirq context, > thus avoiding the need for ksoftirqd to be scheduled. > > Normal waitqueues make use of spinlocks, which on -RT > are sleepable locks. Therefore, waking up a waitqueue > waiter involves locking a sleeping lock, which > is not allowed from hard interrupt context. > What are the consequences for the realtime kernel of making waitqueue traversal non-preemptible? Is waitqueue traversal something that ever takes so long we need to care about it being non-preemptible? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists