From: Paolo Bonzini <pbonzini@redhat.com>
To: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
Cc: jan.kiszka@web.de, qemu-devel@nongnu.org,
aneesh.kumar@linux.vnet.ibm.com
Subject: Re: [Qemu-devel] [PATCH v2 1/2] Introduce QLIST_INSERT_HEAD_RCU and dummy RCU wrappers.
Date: Fri, 14 Oct 2011 08:49:49 +0200 [thread overview]
Message-ID: <4E97DB8D.4070403@redhat.com> (raw)
In-Reply-To: <1318538102-6982-1-git-send-email-harsh@linux.vnet.ibm.com>
On 10/13/2011 10:35 PM, Harsh Prateek Bora wrote:
>
> +#define QLIST_INSERT_HEAD_RCU(head, elm, field) do { \
> + (elm)->field.le_prev =&(head)->lh_first; \
> + smp_wmb(); \
> + if (((elm)->field.le_next = (head)->lh_first) != NULL) \
> + (head)->lh_first->field.le_prev =&(elm)->field.le_next;\
> + smp_wmb(); \
> + (head)->lh_first = (elm); \
> + smp_wmb(); \
> +} while (/* CONSTCOND*/0)
Actually, looking more at it it should be more like
(elm)->field.le_prev =&(head)->lh_first;
(elm)->field.le_next = (head)->lh_first;
smb_wmb(); /* fill elm before linking it */
if ((head)->lh_first != NULL)
(head)->lh_first->field.le_prev =&(elm)->field.le_next;
(head)->lh_first = (elm);
smp_wmb();
... which even saves a memory barrier.
Paolo
prev parent reply other threads:[~2011-10-14 6:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-13 20:35 [Qemu-devel] [PATCH v2 1/2] Introduce QLIST_INSERT_HEAD_RCU and dummy RCU wrappers Harsh Prateek Bora
2011-10-13 20:35 ` [Qemu-devel] [PATCH v2 2/2] Replace rwlocks with RCU variants of interfaces Harsh Prateek Bora
2011-10-13 22:09 ` Harsh Bora
2011-10-14 4:56 ` Aneesh Kumar K.V
2011-10-14 6:49 ` Paolo Bonzini [this message]
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