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Message-Id: <1219209684.21386.21.camel@pasglop>
Date: Wed, 20 Aug 2008 15:21:24 +1000
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: Sebastien Dugue <sebastien.dugue@...l.net>
Cc: linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
linux-rt-users@...r.kernel.org, paulus@...ba.org,
michael@...erman.id.au, jean-pierre.dion@...l.net,
gilles.carry@....bull.net, tinytim@...ibm.com, tglx@...utronix.de,
rostedt@...dmis.org, dwalker@...sta.com
Subject: Re: [PATCH 1/2] powerpc - Separate the irq radix tree insertion
and lookup
On Wed, 2008-08-06 at 15:30 +0200, Sebastien Dugue wrote:
> irq_radix_revmap() currently serves 2 purposes, irq mapping lookup
> and insertion which happen in interrupt and process context respectively.
Sounds good, a few nits and it should be good to go.
> Separate the function into its 2 components, one for lookup only and one
> for insertion only.
>
> Fix the only user of the revmap tree (XICS) to use the new functions.
>
> Also, move the insertion into the radix tree of those irqs that were
> requested before it was initialized at said tree initialization.
>
> Mutual exclusion between the tree initialization and readers/writers is
> handled via an atomic variable (revmap_trees_allocated) set when the tree
> has been initialized and checked before any reader or writer access just
> like we used to check for tree.gfp_mask != 0 before.
The atomic doesn't need to be such. Could just be a global. In fact, I
don't like your synchronization too much between the init and _insert.
What I'd do is, turn your atomic into a simple int
- do smp_wmb() and set it to 1 after the tree is initialized, then
smb_wmb() again and set it to 2 after the tree has been filled
by the init code
- in the revmap_lookup path just test that it's >1, no need for a
barrier. At worst you'll use the slow path instead of the fast path some
time during boot, no big deal.
- in the insert path, do an smp_rb() and if it's >0 do the insert with
the lock
- in the init pre-insert path, use the lock inside the loop for each
insertion.
that means you may get concurrent attempt to insert but the lock will
help there and turn them into 2 insertions of the same translation. Is
that a big deal ? If it is, make it be a lookup+insert.
Ben.
>
> Signed-off-by: Sebastien Dugue <sebastien.dugue@...l.net>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Michael Ellerman <michael@...erman.id.au>
> ---
> arch/powerpc/include/asm/irq.h | 18 ++++++-
> arch/powerpc/kernel/irq.c | 76 ++++++++++++++++++++++++---------
> arch/powerpc/platforms/pseries/xics.c | 11 ++---
> 3 files changed, 74 insertions(+), 31 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
> index a372f76..0a51376 100644
> --- a/arch/powerpc/include/asm/irq.h
> +++ b/arch/powerpc/include/asm/irq.h
> @@ -236,15 +236,27 @@ extern unsigned int irq_find_mapping(struct irq_host *host,
> extern unsigned int irq_create_direct_mapping(struct irq_host *host);
>
> /**
> - * irq_radix_revmap - Find a linux virq from a hw irq number.
> + * irq_radix_revmap_insert - Insert a hw irq to linux virq number mapping.
> + * @host: host owning this hardware interrupt
> + * @virq: linux irq number
> + * @hwirq: hardware irq number in that host space
> + *
> + * This is for use by irq controllers that use a radix tree reverse
> + * mapping for fast lookup.
> + */
> +extern void irq_radix_revmap_insert(struct irq_host *host, unsigned int virq,
> + irq_hw_number_t hwirq);
> +
> +/**
> + * irq_radix_revmap_lookup - Find a linux virq from a hw irq number.
> * @host: host owning this hardware interrupt
> * @hwirq: hardware irq number in that host space
> *
> * This is a fast path, for use by irq controller code that uses radix tree
> * revmaps
> */
> -extern unsigned int irq_radix_revmap(struct irq_host *host,
> - irq_hw_number_t hwirq);
> +extern unsigned int irq_radix_revmap_lookup(struct irq_host *host,
> + irq_hw_number_t hwirq);
>
> /**
> * irq_linear_revmap - Find a linux virq from a hw irq number.
> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
> index d972dec..dc8663a 100644
> --- a/arch/powerpc/kernel/irq.c
> +++ b/arch/powerpc/kernel/irq.c
> @@ -441,6 +441,7 @@ static LIST_HEAD(irq_hosts);
> static DEFINE_SPINLOCK(irq_big_lock);
> static DEFINE_PER_CPU(unsigned int, irq_radix_reader);
> static unsigned int irq_radix_writer;
> +static atomic_t revmap_trees_allocated = ATOMIC_INIT(0);
> struct irq_map_entry irq_map[NR_IRQS];
> static unsigned int irq_virq_count = NR_IRQS;
> static struct irq_host *irq_default_host;
> @@ -822,7 +823,7 @@ void irq_dispose_mapping(unsigned int virq)
> break;
> case IRQ_HOST_MAP_TREE:
> /* Check if radix tree allocated yet */
> - if (host->revmap_data.tree.gfp_mask == 0)
> + if (atomic_read(&revmap_trees_allocated) == 0)
> break;
> irq_radix_wrlock(&flags);
> radix_tree_delete(&host->revmap_data.tree, hwirq);
> @@ -875,43 +876,55 @@ unsigned int irq_find_mapping(struct irq_host *host,
> EXPORT_SYMBOL_GPL(irq_find_mapping);
>
>
> -unsigned int irq_radix_revmap(struct irq_host *host,
> - irq_hw_number_t hwirq)
> +unsigned int irq_radix_revmap_lookup(struct irq_host *host,
> + irq_hw_number_t hwirq)
> {
> - struct radix_tree_root *tree;
> struct irq_map_entry *ptr;
> - unsigned int virq;
> + unsigned int virq = NO_IRQ;
> unsigned long flags;
>
> WARN_ON(host->revmap_type != IRQ_HOST_MAP_TREE);
>
> - /* Check if the radix tree exist yet. We test the value of
> - * the gfp_mask for that. Sneaky but saves another int in the
> - * structure. If not, we fallback to slow mode
> + /*
> + * Check if the radix tree exist yet.
> + * If not, we fallback to slow mode
> */
> - tree = &host->revmap_data.tree;
> - if (tree->gfp_mask == 0)
> + if (atomic_read(&revmap_trees_allocated) == 0)
> return irq_find_mapping(host, hwirq);
>
> /* Now try to resolve */
> irq_radix_rdlock(&flags);
> - ptr = radix_tree_lookup(tree, hwirq);
> + ptr = radix_tree_lookup(&host->revmap_data.tree, hwirq);
> irq_radix_rdunlock(flags);
>
> /* Found it, return */
> - if (ptr) {
> + if (ptr)
> virq = ptr - irq_map;
> - return virq;
> - }
>
> - /* If not there, try to insert it */
> - virq = irq_find_mapping(host, hwirq);
> + return virq;
> +}
> +
> +void irq_radix_revmap_insert(struct irq_host *host, unsigned int virq,
> + irq_hw_number_t hwirq)
> +{
> + unsigned long flags;
> +
> + WARN_ON(host->revmap_type != IRQ_HOST_MAP_TREE);
> +
> + /*
> + * Check if the radix tree exist yet.
> + * If not, then the irq will be inserted into the tree when it gets
> + * initialized.
> + */
> + if (atomic_read(&revmap_trees_allocated) == 0)
> + return;
> +
> if (virq != NO_IRQ) {
> irq_radix_wrlock(&flags);
> - radix_tree_insert(tree, hwirq, &irq_map[virq]);
> + radix_tree_insert(&host->revmap_data.tree, hwirq,
> + &irq_map[virq]);
> irq_radix_wrunlock(flags);
> }
> - return virq;
> }
>
> unsigned int irq_linear_revmap(struct irq_host *host,
> @@ -1020,14 +1033,35 @@ void irq_early_init(void)
> static int irq_late_init(void)
> {
> struct irq_host *h;
> - unsigned long flags;
> + unsigned int i;
>
> - irq_radix_wrlock(&flags);
> + /*
> + * No mutual exclusion with respect to accessors of the tree is needed
> + * here as the synchronization is done via the atomic variable
> + * revmap_trees_allocated.
> + */
> list_for_each_entry(h, &irq_hosts, link) {
> if (h->revmap_type == IRQ_HOST_MAP_TREE)
> INIT_RADIX_TREE(&h->revmap_data.tree, GFP_ATOMIC);
> }
> - irq_radix_wrunlock(flags);
> +
> + /*
> + * Insert the reverse mapping for those interrupts already present
> + * in irq_map[].
> + */
> + for (i = 0; i < irq_virq_count; i++) {
> + if (irq_map[i].host &&
> + (irq_map[i].host->revmap_type == IRQ_HOST_MAP_TREE))
> + radix_tree_insert(&irq_map[i].host->revmap_data.tree,
> + irq_map[i].hwirq, &irq_map[i]);
> + }
> +
> + /*
> + * Make sure the radix trees inits are visible before setting
> + * the flag
> + */
> + smp_mb();
> + atomic_set(&revmap_trees_allocated, 1);
>
> return 0;
> }
> diff --git a/arch/powerpc/platforms/pseries/xics.c b/arch/powerpc/platforms/pseries/xics.c
> index 0fc830f..6b1a005 100644
> --- a/arch/powerpc/platforms/pseries/xics.c
> +++ b/arch/powerpc/platforms/pseries/xics.c
> @@ -310,12 +310,6 @@ static void xics_mask_irq(unsigned int virq)
>
> static unsigned int xics_startup(unsigned int virq)
> {
> - unsigned int irq;
> -
> - /* force a reverse mapping of the interrupt so it gets in the cache */
> - irq = (unsigned int)irq_map[virq].hwirq;
> - irq_radix_revmap(xics_host, irq);
> -
> /* unmask it */
> xics_unmask_irq(virq);
> return 0;
> @@ -346,7 +340,7 @@ static inline unsigned int xics_remap_irq(unsigned int vec)
>
> if (vec == XICS_IRQ_SPURIOUS)
> return NO_IRQ;
> - irq = irq_radix_revmap(xics_host, vec);
> + irq = irq_radix_revmap_lookup(xics_host, vec);
> if (likely(irq != NO_IRQ))
> return irq;
>
> @@ -530,6 +524,9 @@ static int xics_host_map(struct irq_host *h, unsigned int virq,
> {
> pr_debug("xics: map virq %d, hwirq 0x%lx\n", virq, hw);
>
> + /* Insert the interrupt mapping into the radix tree for fast lookup */
> + irq_radix_revmap_insert(xics_host, virq, hw);
> +
> get_irq_desc(virq)->status |= IRQ_LEVEL;
> set_irq_chip_and_handler(virq, xics_irq_chip, handle_fasteoi_irq);
> return 0;
--
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