Messages in this thread | | | From | Barry Song <> | Subject | [PATCH v5 0/3] use bin_attribute to break the size limitation of cpumap ABI | Date | Fri, 2 Jul 2021 21:25:56 +1200 |
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v5: -remove the bitmap API bitmap_print_to_buf, alternatively, only provide cpumap_print_to_buf API as what we really care about is cpumask for this moment. we can freely take bitmap_print_to_buf back once we find the second user. hopefully this can alleviate Yury's worries on possible abuse of a new bitmap API. -correct the document of cpumap_print_to_buf; -In patch1, clearly explain why we need this new API in commit log; -Also refine the commit log of patch 2 and 3; -As the modification is narrowed to the scope of cpumask, the kunit test of bitmap_print_to_buf doesn't apply in the new patchset. so test case patch4/4 is removed.
Thanks for the comments of Greg, Yury, Andy. Thanks for Jonathan's review.
v4: -add test cases for bitmap_print_to_buf API; -add Reviewed-by of Jonathan Cameron for patches 1-3, thanks!
v3: -fixed the strlen issue and patch #1,#2,#3 minor formatting issues, thanks to Andy Shevchenko and Jonathan Cameron.
v2: -split the original patch #1 into two patches and use kasprintf() in -patch #1 to simplify the code. do some minor formatting adjustments.
Background:
the whole story began from this thread when Jonatah and me tried to add a new topology level-cluster which exists on kunpeng920 and X86 Jacobsville: https://lore.kernel.org/lkml/YFRGIedW1fUlnmi+@kroah.com/ https://lore.kernel.org/lkml/YFR2kwakbcGiI37w@kroah.com/
in the discussion, Greg had some concern about the potential one page size limitation of sysfs ABI for topology. Greg's comment is reasonable and I think we should address the problem.
For this moment, numa node, cpu topology and some other drivers are using cpu bitmap and list to expose hardware topology. When cpu number is large, the page buffer of sysfs won't be able to hold the whole bitmask or list. This doesn't really happen nowadays for bitmask as the maximum NR_CPUS is 8196 for X86_64 and 4096 for ARM64 since 8196 * 9 / 32 = 2305 is still smaller than 4KB page size.
So the existing BUILD_BUG_ON() in drivers/base/node.c is pretty much preventing future problems when hardware gets more and more CPUs: static ssize_t node_read_cpumap(struct device *dev, bool list, char *buf) { cpumask_var_t mask; struct node *node_dev = to_node(dev);
/* 2008/04/07: buf currently PAGE_SIZE, need 9 chars per 32 bits. */ BUILD_BUG_ON((NR_CPUS/32 * 9) > (PAGE_SIZE-1)); }
But those ABIs exposing cpu lists are much more tricky as a list could be like: 0, 3, 5, 7, 9, 11... etc. so nobody knows the size till the last moment. Comparing to bitmask, list is easier to exceed one page.
In the previous discussion, Greg and Dave Hansen preferred to remove this kind of limitation totally and remove the BUILD_BUG_ON() in drivers/base/node.c together: https://lore.kernel.org/lkml/1619679819-45256-2-git-send-email-tiantao6@hisilicon.com/ https://lore.kernel.org/lkml/YIueOR4fOYa1dSAb@kroah.com/
Todo:
right now, only topology and node are addressed. there are many other drivers are calling cpumap_print_to_pagebuf() and have the similar problems. we are going to address them one by one after this patchset settles down.
Tian Tao (3): cpumask: introduce cpumap_print_to_buf to support large bitmask and list topology: use bin_attribute to break the size limitation of cpumap ABI drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI
drivers/base/node.c | 52 +++++++++++------- drivers/base/topology.c | 115 ++++++++++++++++++++++------------------ include/linux/cpumask.h | 19 +++++++ lib/cpumask.c | 18 +++++++ 4 files changed, 133 insertions(+), 70 deletions(-)
-- 2.25.1
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