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Message-ID: <20120130215332.GA16747@phenom.dumpdata.com>
Date: Mon, 30 Jan 2012 16:53:32 -0500
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: Wei Liu <wei.liu2@...rix.com>
Cc: netdev@...r.kernel.org, xen-devel@...ts.xensource.com,
ian.campbell@...rix.com
Subject: Re: [RFC PATCH V3 10/16] netback: rework of per-cpu scratch space.
On Mon, Jan 30, 2012 at 02:45:28PM +0000, Wei Liu wrote:
> If we allocate large arrays in per-cpu section, multi-page ring
> feature is likely to blow up the per-cpu section. So avoid allocating
> large arrays, instead we only store pointers to scratch spaces in
> per-cpu section.
>
> CPU hotplug event is also taken care of.
>
> Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> ---
> drivers/net/xen-netback/netback.c | 140 +++++++++++++++++++++++++++----------
> 1 files changed, 104 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> index a8d58a9..2ac9b84 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -39,6 +39,7 @@
> #include <linux/kthread.h>
> #include <linux/if_vlan.h>
> #include <linux/udp.h>
> +#include <linux/cpu.h>
>
> #include <net/tcp.h>
>
> @@ -49,15 +50,15 @@
> #include <asm/xen/page.h>
>
>
> -struct gnttab_copy *tx_copy_ops;
> +DEFINE_PER_CPU(struct gnttab_copy *, tx_copy_ops);
>
> /*
> * Given MAX_BUFFER_OFFSET of 4096 the worst case is that each
> * head/fragment page uses 2 copy operations because it
> * straddles two buffers in the frontend.
> */
> -struct gnttab_copy *grant_copy_op;
> -struct xenvif_rx_meta *meta;
> +DEFINE_PER_CPU(struct gnttab_copy *, grant_copy_op);
> +DEFINE_PER_CPU(struct xenvif_rx_meta *, meta);
>
> static void xenvif_idx_release(struct xenvif *vif, u16 pending_idx);
> static void make_tx_response(struct xenvif *vif,
> @@ -481,8 +482,8 @@ void xenvif_rx_action(struct xenvif *vif)
> struct skb_cb_overlay *sco;
> int need_to_notify = 0;
>
> - struct gnttab_copy *gco = get_cpu_ptr(grant_copy_op);
> - struct xenvif_rx_meta *m = get_cpu_ptr(meta);
> + struct gnttab_copy *gco = get_cpu_var(grant_copy_op);
> + struct xenvif_rx_meta *m = get_cpu_var(meta);
>
> struct netrx_pending_operations npo = {
> .copy = gco,
> @@ -512,8 +513,8 @@ void xenvif_rx_action(struct xenvif *vif)
> BUG_ON(npo.meta_prod > MAX_PENDING_REQS);
>
> if (!npo.copy_prod) {
> - put_cpu_ptr(gco);
> - put_cpu_ptr(m);
> + put_cpu_var(grant_copy_op);
> + put_cpu_var(meta);
> return;
> }
>
> @@ -599,8 +600,8 @@ void xenvif_rx_action(struct xenvif *vif)
> if (!skb_queue_empty(&vif->rx_queue))
> xenvif_kick_thread(vif);
>
> - put_cpu_ptr(gco);
> - put_cpu_ptr(m);
> + put_cpu_var(grant_copy_op);
> + put_cpu_var(meta);
> }
>
> void xenvif_queue_tx_skb(struct xenvif *vif, struct sk_buff *skb)
> @@ -1287,12 +1288,12 @@ int xenvif_tx_action(struct xenvif *vif, int budget)
> if (unlikely(!tx_work_todo(vif)))
> return 0;
>
> - tco = get_cpu_ptr(tx_copy_ops);
> + tco = get_cpu_var(tx_copy_ops);
>
> nr_gops = xenvif_tx_build_gops(vif, tco);
>
> if (nr_gops == 0) {
> - put_cpu_ptr(tco);
> + put_cpu_var(tx_copy_ops);
> return 0;
> }
>
> @@ -1301,7 +1302,7 @@ int xenvif_tx_action(struct xenvif *vif, int budget)
>
> work_done = xenvif_tx_submit(vif, tco, budget);
>
> - put_cpu_ptr(tco);
> + put_cpu_var(tx_copy_ops);
>
> return work_done;
> }
> @@ -1452,31 +1453,97 @@ int xenvif_kthread(void *data)
> return 0;
> }
>
> +static int __create_percpu_scratch_space(unsigned int cpu)
> +{
> + per_cpu(tx_copy_ops, cpu) =
> + vzalloc(sizeof(struct gnttab_copy) * MAX_PENDING_REQS);
> +
> + per_cpu(grant_copy_op, cpu) =
> + vzalloc(sizeof(struct gnttab_copy)
> + * 2 * XEN_NETIF_RX_RING_SIZE);
> +
> + per_cpu(meta, cpu) = vzalloc(sizeof(struct xenvif_rx_meta)
> + * 2 * XEN_NETIF_RX_RING_SIZE);
> +
> + if (!per_cpu(tx_copy_ops, cpu) ||
> + !per_cpu(grant_copy_op, cpu) ||
> + !per_cpu(meta, cpu))
Hm, shouldn't you vfree one at least them? It might be that just one of
them failed.
> + return -ENOMEM;
> +
> + return 0;
> +}
> +
> +static void __free_percpu_scratch_space(unsigned int cpu)
> +{
> + /* freeing NULL pointer is legit */
> + vfree(per_cpu(tx_copy_ops, cpu));
> + vfree(per_cpu(grant_copy_op, cpu));
> + vfree(per_cpu(meta, cpu));
> +}
> +
> +static int __netback_percpu_callback(struct notifier_block *nfb,
> + unsigned long action, void *hcpu)
> +{
> + unsigned int cpu = (unsigned long)hcpu;
> + int rc = NOTIFY_DONE;
> +
> + switch (action) {
> + case CPU_ONLINE:
> + case CPU_ONLINE_FROZEN:
> + printk(KERN_INFO
> + "netback: CPU %x online, creating scratch space\n", cpu);
Is there any way to use 'pr_info(DRV_NAME' for these printk's? It might
require another patch, but it would make it nicer.
> + rc = __create_percpu_scratch_space(cpu);
> + if (rc) {
> + printk(KERN_ALERT
> + "netback: failed to create scratch space for CPU"
> + " %x\n", cpu);
> + /* FIXME: nothing more we can do here, we will
> + * print out warning message when thread or
> + * NAPI runs on this cpu. Also stop getting
> + * called in the future.
> + */
> + __free_percpu_scratch_space(cpu);
> + rc = NOTIFY_BAD;
> + } else {
> + rc = NOTIFY_OK;
> + }
> + break;
> + case CPU_DEAD:
> + case CPU_DEAD_FROZEN:
> + printk("netback: CPU %x offline, destroying scratch space\n",
> + cpu);
pr_debug?
> + __free_percpu_scratch_space(cpu);
> + rc = NOTIFY_OK;
> + break;
> + default:
> + break;
> + }
> +
> + return rc;
> +}
> +
> +static struct notifier_block netback_notifier_block = {
> + .notifier_call = __netback_percpu_callback,
> +};
>
> static int __init netback_init(void)
> {
> int rc = -ENOMEM;
> + int cpu;
>
> if (!xen_domain())
> return -ENODEV;
>
> - tx_copy_ops = __alloc_percpu(sizeof(struct gnttab_copy)
> - * MAX_PENDING_REQS,
> - __alignof__(struct gnttab_copy));
> - if (!tx_copy_ops)
> - goto failed_init;
> + /* Don't need to disable preempt here, since nobody else will
> + * touch these percpu areas during start up. */
> + for_each_online_cpu(cpu) {
> + rc = __create_percpu_scratch_space(cpu);
>
> - grant_copy_op = __alloc_percpu(sizeof(struct gnttab_copy)
> - * 2 * XEN_NETIF_RX_RING_SIZE,
> - __alignof__(struct gnttab_copy));
> - if (!grant_copy_op)
> - goto failed_init_gco;
> + if (rc)
> + goto failed_init;
> + }
>
> - meta = __alloc_percpu(sizeof(struct xenvif_rx_meta)
> - * 2 * XEN_NETIF_RX_RING_SIZE,
> - __alignof__(struct xenvif_rx_meta));
> - if (!meta)
> - goto failed_init_meta;
> + register_hotcpu_notifier(&netback_notifier_block);
>
> rc = page_pool_init();
> if (rc)
> @@ -1491,25 +1558,26 @@ static int __init netback_init(void)
> failed_init_xenbus:
> page_pool_destroy();
> failed_init_pool:
> - free_percpu(meta);
> -failed_init_meta:
> - free_percpu(grant_copy_op);
> -failed_init_gco:
> - free_percpu(tx_copy_ops);
> + for_each_online_cpu(cpu)
> + __free_percpu_scratch_space(cpu);
> failed_init:
> return rc;
We don't want to try to clean up the per_cpu_spaces that might
have gotten allocated in the loop?
> -
> }
>
> module_init(netback_init);
>
> static void __exit netback_exit(void)
> {
> + int cpu;
> +
> xenvif_xenbus_exit();
> page_pool_destroy();
> - free_percpu(meta);
> - free_percpu(grant_copy_op);
> - free_percpu(tx_copy_ops);
> +
> + unregister_hotcpu_notifier(&netback_notifier_block);
> +
> + /* Since we're here, nobody else will touch per-cpu area. */
> + for_each_online_cpu(cpu)
> + __free_percpu_scratch_space(cpu);
> }
> module_exit(netback_exit);
>
> --
> 1.7.2.5
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