From 9ccfacd4706c785434848b9b31701945eceefe0f Mon Sep 17 00:00:00 2001 From: Tim Deegan Date: Thu, 15 Mar 2012 11:12:44 +0000 Subject: [PATCH] x86/mm: Allow to not sleep on mem event ring Under extreme congestion conditions, generating a mem event may put the vcpu to sleep on a wait queue if the ring is full. This is generally desirable, although fairly convoluted to work with, since sleeping on a wait queue requires a non-atomic context (i.e. no locks held). Introduce an allow_sleep flag to make this optional. The default API remains such that all current callers set allow_sleep to true and thus will sleep if necessary. The end-use is for cases in which loss of guest mem events is tolerable. One such consumer to be added later is the unsharing code under ENOMEM conditions. Signed-off-by: Andres Lagar-Cavilla Signed-off-by: Adin Scannell Acked-by: Tim Deegan Committed-by: Tim Deegan --- xen/arch/x86/mm/mem_event.c | 5 +++-- xen/include/asm-x86/mem_event.h | 30 +++++++++++++++++++++++++----- 2 files changed, 28 insertions(+), 7 deletions(-) diff --git a/xen/arch/x86/mm/mem_event.c b/xen/arch/x86/mm/mem_event.c index ff644790be..4e01c7ff21 100644 --- a/xen/arch/x86/mm/mem_event.c +++ b/xen/arch/x86/mm/mem_event.c @@ -409,9 +409,10 @@ bool_t mem_event_check_ring(struct mem_event_domain *med) * 0: a spot has been reserved * */ -int mem_event_claim_slot(struct domain *d, struct mem_event_domain *med) +int __mem_event_claim_slot(struct domain *d, struct mem_event_domain *med, + bool_t allow_sleep) { - if ( current->domain == d ) + if ( (current->domain == d) && allow_sleep ) return mem_event_wait_slot(med); else return mem_event_grab_slot(med, 1); diff --git a/xen/include/asm-x86/mem_event.h b/xen/include/asm-x86/mem_event.h index 3111ce77d2..23d71c1d8e 100644 --- a/xen/include/asm-x86/mem_event.h +++ b/xen/include/asm-x86/mem_event.h @@ -28,11 +28,31 @@ bool_t mem_event_check_ring(struct mem_event_domain *med); /* Returns 0 on success, -ENOSYS if there is no ring, -EBUSY if there is no - * available space. For success or -EBUSY, the vCPU may be left blocked - * temporarily to ensure that the ring does not lose future events. In - * general, you must follow a claim_slot() call with either put_request() or - * cancel_slot(), both of which are guaranteed to succeed. */ -int mem_event_claim_slot(struct domain *d, struct mem_event_domain *med); + * available space and the caller is a foreign domain. If the guest itself + * is the caller, -EBUSY is avoided by sleeping on a wait queue to ensure + * that the ring does not lose future events. + * + * However, the allow_sleep flag can be set to false in cases in which it is ok + * to lose future events, and thus -EBUSY can be returned to guest vcpus + * (handle with care!). + * + * In general, you must follow a claim_slot() call with either put_request() or + * cancel_slot(), both of which are guaranteed to + * succeed. + */ +int __mem_event_claim_slot(struct domain *d, struct mem_event_domain *med, + bool_t allow_sleep); +static inline int mem_event_claim_slot(struct domain *d, + struct mem_event_domain *med) +{ + return __mem_event_claim_slot(d, med, 1); +} + +static inline int mem_event_claim_slot_nosleep(struct domain *d, + struct mem_event_domain *med) +{ + return __mem_event_claim_slot(d, med, 0); +} void mem_event_cancel_slot(struct domain *d, struct mem_event_domain *med); -- 2.39.5