From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien.grall@arm.com>
Cc: sstabellini@kernel.org, wei.chen@linaro.org,
shankerd@codeaurora.org, xen-devel@lists.xen.org
Subject: Re: [PATCH] xen/arm: io: Protect the handlers with a read-write lock
Date: Mon, 11 Jul 2016 18:49:34 +0100 (BST) [thread overview]
Message-ID: <alpine.DEB.2.10.1607111844460.26575@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <1467131671-24612-1-git-send-email-julien.grall@arm.com>
On Tue, 28 Jun 2016, Julien Grall wrote:
> Currently, accessing the I/O handlers does not require to take a lock
> because new handlers are always added at the end of the array. In a
> follow-up patch, this array will be sort to optimize the look up.
>
> Given that most of the time the I/O handlers will not be modify,
> using a spinlock will add contention when multiple vCPU are accessing
> the emulated MMIOs. So use a read-write lock to protected the handlers.
>
> Finally, take the opportunity to re-indent correctly domain_io_init.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
I would appreciate if you could avoid mixing indentation changes with
other changes in the future.
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
I'll commit.
> xen/arch/arm/io.c | 47 +++++++++++++++++++++++++++-------------------
> xen/include/asm-arm/mmio.h | 3 ++-
> 2 files changed, 30 insertions(+), 20 deletions(-)
>
> diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
> index 0156755..5a96836 100644
> --- a/xen/arch/arm/io.c
> +++ b/xen/arch/arm/io.c
> @@ -70,23 +70,39 @@ static int handle_write(const struct mmio_handler *handler, struct vcpu *v,
> handler->priv);
> }
>
> -int handle_mmio(mmio_info_t *info)
> +static const struct mmio_handler *find_mmio_handler(struct domain *d,
> + paddr_t gpa)
> {
> - struct vcpu *v = current;
> - int i;
> - const struct mmio_handler *handler = NULL;
> - const struct vmmio *vmmio = &v->domain->arch.vmmio;
> + const struct mmio_handler *handler;
> + unsigned int i;
> + struct vmmio *vmmio = &d->arch.vmmio;
> +
> + read_lock(&vmmio->lock);
>
> for ( i = 0; i < vmmio->num_entries; i++ )
> {
> handler = &vmmio->handlers[i];
>
> - if ( (info->gpa >= handler->addr) &&
> - (info->gpa < (handler->addr + handler->size)) )
> + if ( (gpa >= handler->addr) &&
> + (gpa < (handler->addr + handler->size)) )
> break;
> }
>
> if ( i == vmmio->num_entries )
> + handler = NULL;
> +
> + read_unlock(&vmmio->lock);
> +
> + return handler;
> +}
> +
> +int handle_mmio(mmio_info_t *info)
> +{
> + struct vcpu *v = current;
> + const struct mmio_handler *handler = NULL;
> +
> + handler = find_mmio_handler(v->domain, info->gpa);
> + if ( !handler )
> return 0;
>
> if ( info->dabt.write )
> @@ -104,7 +120,7 @@ void register_mmio_handler(struct domain *d,
>
> BUG_ON(vmmio->num_entries >= MAX_IO_HANDLER);
>
> - spin_lock(&vmmio->lock);
> + write_lock(&vmmio->lock);
>
> handler = &vmmio->handlers[vmmio->num_entries];
>
> @@ -113,24 +129,17 @@ void register_mmio_handler(struct domain *d,
> handler->size = size;
> handler->priv = priv;
>
> - /*
> - * handle_mmio is not using the lock to avoid contention.
> - * Make sure the other processors see the new handler before
> - * updating the number of entries
> - */
> - dsb(ish);
> -
> vmmio->num_entries++;
>
> - spin_unlock(&vmmio->lock);
> + write_unlock(&vmmio->lock);
> }
>
> int domain_io_init(struct domain *d)
> {
> - spin_lock_init(&d->arch.vmmio.lock);
> - d->arch.vmmio.num_entries = 0;
> + rwlock_init(&d->arch.vmmio.lock);
> + d->arch.vmmio.num_entries = 0;
>
> - return 0;
> + return 0;
> }
>
> /*
> diff --git a/xen/include/asm-arm/mmio.h b/xen/include/asm-arm/mmio.h
> index da1cc2e..32f10f2 100644
> --- a/xen/include/asm-arm/mmio.h
> +++ b/xen/include/asm-arm/mmio.h
> @@ -20,6 +20,7 @@
> #define __ASM_ARM_MMIO_H__
>
> #include <xen/lib.h>
> +#include <xen/rwlock.h>
> #include <asm/processor.h>
> #include <asm/regs.h>
>
> @@ -51,7 +52,7 @@ struct mmio_handler {
>
> struct vmmio {
> int num_entries;
> - spinlock_t lock;
> + rwlock_t lock;
> struct mmio_handler handlers[MAX_IO_HANDLER];
> };
>
> --
> 1.9.1
>
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next prev parent reply other threads:[~2016-07-11 17:49 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-28 16:34 [PATCH] xen/arm: io: Protect the handlers with a read-write lock Julien Grall
2016-07-11 17:49 ` Stefano Stabellini [this message]
2016-07-11 18:07 ` Julien Grall
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