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Date: Tue, 5 May 2020 11:18:39 +0200
From: Emanuele Giuseppe Esposito <eesposit@...hat.com>
To: David Rientjes <rientjes@...gle.com>
Cc: Jonathan Adams <jwadams@...gle.com>, kvm@...r.kernel.org,
Christian Borntraeger <borntraeger@...ibm.com>,
David Hildenbrand <david@...hat.com>,
Cornelia Huck <cohuck@...hat.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Emanuele Giuseppe Esposito <e.emanuelegiuseppe@...il.com>,
linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
kvm-ppc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 0/5] Statsfs: a new ram-based file sytem for Linux
kernel statistics
On 5/4/20 11:37 PM, David Rientjes wrote:
> On Mon, 4 May 2020, Emanuele Giuseppe Esposito wrote:
>
>>
>> In this patch series I introduce statsfs, a synthetic ram-based virtual
>> filesystem that takes care of gathering and displaying statistics for the
>> Linux kernel subsystems.
>>
>
> This is exciting, we have been looking in the same area recently. Adding
> Jonathan Adams <jwadams@...gle.com>.
>
> In your diffstat, one thing I notice that is omitted: an update to
> Documentation/* :) Any chance of getting some proposed Documentation/
> updates with structure of the fs, the per subsystem breakdown, and best
> practices for managing the stats from the kernel level?
Yes, I will write some documentation. Thank you for the suggestion.
>>
>> Values represent quantites that are gathered by the statsfs user. Examples
>> of values include the number of vm exits of a given kind, the amount of
>> memory used by some data structure, the length of the longest hash table
>> chain, or anything like that. Values are defined with the
>> statsfs_source_add_values function. Each value is defined by a struct
>> statsfs_value; the same statsfs_value can be added to many different
>> sources. A value can be considered "simple" if it fetches data from a
>> user-provided location, or "aggregate" if it groups all values in the
>> subordinates sources that include the same statsfs_value.
>>
>
> This seems like it could have a lot of overhead if we wanted to
> periodically track the totality of subsystem stats as a form of telemetry
> gathering from userspace. To collect telemetry for 1,000 different stats,
> do we need to issue lseek()+read() syscalls for each of them individually
> (or, worse, open()+read()+close())?
>
> Any thoughts on how that can be optimized? A couple of ideas:
>
> - an interface that allows gathering of all stats for a particular
> interface through a single file that would likely be encoded in binary
> and the responsibility of userspace to disseminate, or
>
> - an interface that extends beyond this proposal and allows the reader to
> specify which stats they are interested in collecting and then the
> kernel will only provide these stats in a well formed structure and
> also be binary encoded.
Are you thinking of another file, containing all the stats for the
directory in binary format?
> We've found that the one-file-per-stat method is pretty much a show
> stopper from the performance view and we always must execute at least two
> syscalls to obtain a single stat.
>
> Since this is becoming a generic API (good!!), maybe we can discuss
> possible ways to optimize gathering of stats in mass?
Sure, the idea of a binary format was considered from the beginning in
[1], and it can be done either together with the current filesystem, or
as a replacement via different mount options.
Thank you,
Emanuele
>> [1] https://lore.kernel.org/kvm/5d6cdcb1-d8ad-7ae6-7351-3544e2fa366d@redhat.com/?fbclid=IwAR18LHJ0PBcXcDaLzILFhHsl3qpT3z2vlG60RnqgbpGYhDv7L43n0ZXJY8M
>>
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@...hat.com>
>>
>> v1->v2 remove unnecessary list_foreach_safe loops, fix wrong indentation,
>> change statsfs in stats_fs
>>
>> Emanuele Giuseppe Esposito (5):
>> refcount, kref: add dec-and-test wrappers for rw_semaphores
>> stats_fs API: create, add and remove stats_fs sources and values
>> kunit: tests for stats_fs API
>> stats_fs fs: virtual fs to show stats to the end-user
>> kvm_main: replace debugfs with stats_fs
>>
>> MAINTAINERS | 7 +
>> arch/arm64/kvm/Kconfig | 1 +
>> arch/arm64/kvm/guest.c | 2 +-
>> arch/mips/kvm/Kconfig | 1 +
>> arch/mips/kvm/mips.c | 2 +-
>> arch/powerpc/kvm/Kconfig | 1 +
>> arch/powerpc/kvm/book3s.c | 6 +-
>> arch/powerpc/kvm/booke.c | 8 +-
>> arch/s390/kvm/Kconfig | 1 +
>> arch/s390/kvm/kvm-s390.c | 16 +-
>> arch/x86/include/asm/kvm_host.h | 2 +-
>> arch/x86/kvm/Kconfig | 1 +
>> arch/x86/kvm/Makefile | 2 +-
>> arch/x86/kvm/debugfs.c | 64 --
>> arch/x86/kvm/stats_fs.c | 56 ++
>> arch/x86/kvm/x86.c | 6 +-
>> fs/Kconfig | 12 +
>> fs/Makefile | 1 +
>> fs/stats_fs/Makefile | 6 +
>> fs/stats_fs/inode.c | 337 ++++++++++
>> fs/stats_fs/internal.h | 35 +
>> fs/stats_fs/stats_fs-tests.c | 1088 +++++++++++++++++++++++++++++++
>> fs/stats_fs/stats_fs.c | 773 ++++++++++++++++++++++
>> include/linux/kref.h | 11 +
>> include/linux/kvm_host.h | 39 +-
>> include/linux/refcount.h | 2 +
>> include/linux/stats_fs.h | 304 +++++++++
>> include/uapi/linux/magic.h | 1 +
>> lib/refcount.c | 32 +
>> tools/lib/api/fs/fs.c | 21 +
>> virt/kvm/arm/arm.c | 2 +-
>> virt/kvm/kvm_main.c | 314 ++-------
>> 32 files changed, 2772 insertions(+), 382 deletions(-)
>> delete mode 100644 arch/x86/kvm/debugfs.c
>> create mode 100644 arch/x86/kvm/stats_fs.c
>> create mode 100644 fs/stats_fs/Makefile
>> create mode 100644 fs/stats_fs/inode.c
>> create mode 100644 fs/stats_fs/internal.h
>> create mode 100644 fs/stats_fs/stats_fs-tests.c
>> create mode 100644 fs/stats_fs/stats_fs.c
>> create mode 100644 include/linux/stats_fs.h
>>
>> --
>> 2.25.2
>>
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