-Chintan On 12/12/19 5:50 AM, Frank Rowand wrote: > > +Chintan > > Hi Chintan, > > On 12/11/19 5:23 PM, Rob Herring wrote: >> The phandle cache was added to speed up of_find_node_by_phandle() by >> avoiding walking the whole DT to find a matching phandle. The >> implementation has several shortcomings: >> >> - The cache is designed to work on a linear set of phandle values. >> This is true for dtc generated DTs, but not for other cases such as >> Power. >> - The cache isn't enabled until of_core_init() and a typical system >> may see hundreds of calls to of_find_node_by_phandle() before that >> point. >> - The cache is freed and re-allocated when the number of phandles >> changes. >> - It takes a raw spinlock around a memory allocation which breaks on >> RT. >> >> Change the implementation to a fixed size and use hash_32() as the >> cache index. This greatly simplifies the implementation. It avoids >> the need for any re-alloc of the cache and taking a reference on nodes >> in the cache. We only have a single source of removing cache entries >> which is of_detach_node(). > > Can you check this patch on the system that you reported phandle lookup > overhead issues for? Adding Chintan to the distribution list was not successful -- his email address bounces. If anyone else from Qualcomm wants to look at this, the system Chintan was measuring was: https://source.codeaurora.org/quic/la/kernel/msm-4.9/tree/arch/arm64/boot/dts/qcom/sda670-mtp.dts?h=msm-4.9 The various email threads were in January and February 2018. -Frank > > -Frank > > >> >> Using hash_32() removes any assumption on phandle values improving >> the hit rate for non-linear phandle values. The effect on linear values >> using hash_32() is about a 10% collision. The chances of thrashing on >> colliding values seems to be low. >> >> To compare performance, I used a RK3399 board which is a pretty typical >> system. I found that just measuring boot time as done previously is >> noisy and may be impacted by other things. Also bringing up secondary >> cores causes some issues with measuring, so I booted with 'nr_cpus=1'. >> With no caching, calls to of_find_node_by_phandle() take about 20124 us >> for 1248 calls. There's an additional 288 calls before time keeping is >> up. Using the average time per hit/miss with the cache, we can calculate >> these calls to take 690 us (277 hit / 11 miss) with a 128 entry cache >> and 13319 us with no cache or an uninitialized cache. >> >> Comparing the 3 implementations the time spent in >> of_find_node_by_phandle() is: >> >> no cache: 20124 us (+ 13319 us) >> 128 entry cache: 5134 us (+ 690 us) >> current cache: 819 us (+ 13319 us) >> >> We could move the allocation of the cache earlier to improve the >> current cache, but that just further complicates the situation as it >> needs to be after slab is up, so we can't do it when unflattening (which >> uses memblock). >> >> Reported-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> >> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> >> Cc: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> >> Cc: Frank Rowand <frowand.list@xxxxxxxxx> >> Signed-off-by: Rob Herring <robh@xxxxxxxxxx> >> --- >> drivers/of/base.c | 133 ++++++++-------------------------------- >> drivers/of/dynamic.c | 2 +- >> drivers/of/of_private.h | 4 +- >> drivers/of/overlay.c | 10 --- >> 4 files changed, 28 insertions(+), 121 deletions(-) >> >> diff --git a/drivers/of/base.c b/drivers/of/base.c >> index db7fbc0c0893..f7da162f126d 100644 >> --- a/drivers/of/base.c >> +++ b/drivers/of/base.c >> @@ -135,115 +135,38 @@ int __weak of_node_to_nid(struct device_node *np) >> } >> #endif >> >> -/* >> - * Assumptions behind phandle_cache implementation: >> - * - phandle property values are in a contiguous range of 1..n >> - * >> - * If the assumptions do not hold, then >> - * - the phandle lookup overhead reduction provided by the cache >> - * will likely be less >> - */ >> +#define OF_PHANDLE_CACHE_BITS 7 >> +#define OF_PHANDLE_CACHE_SZ BIT(OF_PHANDLE_CACHE_BITS) >> >> -static struct device_node **phandle_cache; >> -static u32 phandle_cache_mask; >> +static struct device_node *phandle_cache[OF_PHANDLE_CACHE_SZ]; >> >> -/* >> - * Caller must hold devtree_lock. >> - */ >> -static void __of_free_phandle_cache(void) >> +static u32 of_phandle_cache_hash(phandle handle) >> { >> - u32 cache_entries = phandle_cache_mask + 1; >> - u32 k; >> - >> - if (!phandle_cache) >> - return; >> - >> - for (k = 0; k < cache_entries; k++) >> - of_node_put(phandle_cache[k]); >> - >> - kfree(phandle_cache); >> - phandle_cache = NULL; >> + return hash_32(handle, OF_PHANDLE_CACHE_BITS); >> } >> >> -int of_free_phandle_cache(void) >> -{ >> - unsigned long flags; >> - >> - raw_spin_lock_irqsave(&devtree_lock, flags); >> - >> - __of_free_phandle_cache(); >> - >> - raw_spin_unlock_irqrestore(&devtree_lock, flags); >> - >> - return 0; >> -} >> -#if !defined(CONFIG_MODULES) >> -late_initcall_sync(of_free_phandle_cache); >> -#endif >> - >> /* >> * Caller must hold devtree_lock. >> */ >> -void __of_free_phandle_cache_entry(phandle handle) >> +void __of_phandle_cache_inv_entry(phandle handle) >> { >> - phandle masked_handle; >> + u32 handle_hash; >> struct device_node *np; >> >> if (!handle) >> return; >> >> - masked_handle = handle & phandle_cache_mask; >> + handle_hash = of_phandle_cache_hash(handle); >> >> - if (phandle_cache) { >> - np = phandle_cache[masked_handle]; >> - if (np && handle == np->phandle) { >> - of_node_put(np); >> - phandle_cache[masked_handle] = NULL; >> - } >> - } >> -} >> - >> -void of_populate_phandle_cache(void) >> -{ >> - unsigned long flags; >> - u32 cache_entries; >> - struct device_node *np; >> - u32 phandles = 0; >> - >> - raw_spin_lock_irqsave(&devtree_lock, flags); >> - >> - __of_free_phandle_cache(); >> - >> - for_each_of_allnodes(np) >> - if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL) >> - phandles++; >> - >> - if (!phandles) >> - goto out; >> - >> - cache_entries = roundup_pow_of_two(phandles); >> - phandle_cache_mask = cache_entries - 1; >> - >> - phandle_cache = kcalloc(cache_entries, sizeof(*phandle_cache), >> - GFP_ATOMIC); >> - if (!phandle_cache) >> - goto out; >> - >> - for_each_of_allnodes(np) >> - if (np->phandle && np->phandle != OF_PHANDLE_ILLEGAL) { >> - of_node_get(np); >> - phandle_cache[np->phandle & phandle_cache_mask] = np; >> - } >> - >> -out: >> - raw_spin_unlock_irqrestore(&devtree_lock, flags); >> + np = phandle_cache[handle_hash]; >> + if (np && handle == np->phandle) >> + phandle_cache[handle_hash] = NULL; >> } >> >> void __init of_core_init(void) >> { >> struct device_node *np; >> >> - of_populate_phandle_cache(); >> >> /* Create the kset, and register existing nodes */ >> mutex_lock(&of_mutex); >> @@ -253,8 +176,11 @@ void __init of_core_init(void) >> pr_err("failed to register existing nodes\n"); >> return; >> } >> - for_each_of_allnodes(np) >> + for_each_of_allnodes(np) { >> __of_attach_node_sysfs(np); >> + if (np->phandle && !phandle_cache[of_phandle_cache_hash(np->phandle)]) >> + phandle_cache[of_phandle_cache_hash(np->phandle)] = np; >> + } >> mutex_unlock(&of_mutex); >> >> /* Symlink in /proc as required by userspace ABI */ >> @@ -1235,36 +1161,29 @@ struct device_node *of_find_node_by_phandle(phandle handle) >> { >> struct device_node *np = NULL; >> unsigned long flags; >> - phandle masked_handle; >> + u32 handle_hash; >> >> if (!handle) >> return NULL; >> >> + handle_hash = of_phandle_cache_hash(handle); >> + >> raw_spin_lock_irqsave(&devtree_lock, flags); >> >> - masked_handle = handle & phandle_cache_mask; >> - >> - if (phandle_cache) { >> - if (phandle_cache[masked_handle] && >> - handle == phandle_cache[masked_handle]->phandle) >> - np = phandle_cache[masked_handle]; >> - if (np && of_node_check_flag(np, OF_DETACHED)) { >> - WARN_ON(1); /* did not uncache np on node removal */ >> - of_node_put(np); >> - phandle_cache[masked_handle] = NULL; >> - np = NULL; >> - } >> + if (phandle_cache[handle_hash] && >> + handle == phandle_cache[handle_hash]->phandle) >> + np = phandle_cache[handle_hash]; >> + if (np && of_node_check_flag(np, OF_DETACHED)) { >> + WARN_ON(1); /* did not uncache np on node removal */ >> + phandle_cache[handle_hash] = NULL; >> + np = NULL; >> } >> >> if (!np) { >> for_each_of_allnodes(np) >> if (np->phandle == handle && >> !of_node_check_flag(np, OF_DETACHED)) { >> - if (phandle_cache) { >> - /* will put when removed from cache */ >> - of_node_get(np); >> - phandle_cache[masked_handle] = np; >> - } >> + phandle_cache[handle_hash] = np; >> break; >> } >> } >> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c >> index 49b16f76d78e..08fd823edac9 100644 >> --- a/drivers/of/dynamic.c >> +++ b/drivers/of/dynamic.c >> @@ -276,7 +276,7 @@ void __of_detach_node(struct device_node *np) >> of_node_set_flag(np, OF_DETACHED); >> >> /* race with of_find_node_by_phandle() prevented by devtree_lock */ >> - __of_free_phandle_cache_entry(np->phandle); >> + __of_phandle_cache_inv_entry(np->phandle); >> } >> >> /** >> diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h >> index 66294d29942a..582844c158ae 100644 >> --- a/drivers/of/of_private.h >> +++ b/drivers/of/of_private.h >> @@ -85,14 +85,12 @@ int of_resolve_phandles(struct device_node *tree); >> #endif >> >> #if defined(CONFIG_OF_DYNAMIC) >> -void __of_free_phandle_cache_entry(phandle handle); >> +void __of_phandle_cache_inv_entry(phandle handle); >> #endif >> >> #if defined(CONFIG_OF_OVERLAY) >> void of_overlay_mutex_lock(void); >> void of_overlay_mutex_unlock(void); >> -int of_free_phandle_cache(void); >> -void of_populate_phandle_cache(void); >> #else >> static inline void of_overlay_mutex_lock(void) {}; >> static inline void of_overlay_mutex_unlock(void) {}; >> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c >> index 9617b7df7c4d..97fe92c1f1d2 100644 >> --- a/drivers/of/overlay.c >> +++ b/drivers/of/overlay.c >> @@ -974,8 +974,6 @@ static int of_overlay_apply(const void *fdt, struct device_node *tree, >> goto err_free_overlay_changeset; >> } >> >> - of_populate_phandle_cache(); >> - >> ret = __of_changeset_apply_notify(&ovcs->cset); >> if (ret) >> pr_err("overlay apply changeset entry notify error %d\n", ret); >> @@ -1218,17 +1216,9 @@ int of_overlay_remove(int *ovcs_id) >> >> list_del(&ovcs->ovcs_list); >> >> - /* >> - * Disable phandle cache. Avoids race condition that would arise >> - * from removing cache entry when the associated node is deleted. >> - */ >> - of_free_phandle_cache(); >> - >> ret_apply = 0; >> ret = __of_changeset_revert_entries(&ovcs->cset, &ret_apply); >> >> - of_populate_phandle_cache(); >> - >> if (ret) { >> if (ret_apply) >> devicetree_state_flags |= DTSF_REVERT_FAIL; >> > >
