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Date: Tue, 31 Jan 2012 10:48:42 +0000
From: Wei Liu <wei.liu2@...rix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: <wei.liu2@...rix.com>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
"Ian Campbell" <Ian.Campbell@...rix.com>
Subject: Re: [RFC PATCH V3 10/16] netback: rework of per-cpu scratch space.
On Mon, 2012-01-30 at 21:53 +0000, Konrad Rzeszutek Wilk wrote:
> 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.
>
The caller will clean up.
> > + 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.
>
Hmm... will look into that.
> > + 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?
>
Good catch, thanks.
Wei.
> > -
> > }
> >
> > 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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