NACK/Cmnt: [SRU][B][F][G][PATCH 0/1] dm crypt: add flags to optionally

[Stefan Bader]

On 18.05.21 04:56, Gerald Yang wrote:
> BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1910976

Above should be https://bugs.launchpad.net/bugs/1910976 but that could be done 
when applying. However there seem to be multiple references to this patch 
following its introduction upstream (see below). That does not sound like just 
picking this one patch is a good idea.

-Stefan

> 
> === SRU Justification ===
> [Impact]
> To get better performance for dm-crypt in some cases, bypass kcryptd
> workqueue can reduce the overhead in context switch between kworkers,
> cherry-pick commit 39d42fa96ba1b7d2544db3f8ed5da8fb0d5cb877 from mainline
> kernel, and bypass kcryptd workqueue is not enabled by default
> 
> [Fix]
> Add flags to bypass kcryptd workqueue
> 
> [Test]
> create dm-crypt and setup DM_CRYPT_NO_READ_WORKQUEUE and
> DM_CRYPT_NO_WRITE_WORKQUEUE, read/write data and run perf record to see
> if read/write to the encrypted device will bypass kcryptd workqueue
> 
> [Regression Potential]
> Low, this feature is disabled by default, need to enable manually
> 
> Ignat Korchagin (1):
>    dm crypt: add flags to optionally bypass kcryptd workqueues
> 
>   drivers/md/dm-crypt.c | 50 ++++++++++++++++++++++++++++++++++++-------
>   1 file changed, 42 insertions(+), 8 deletions(-)
> 

 > git log --oneline --grep "Fixes: 39d42fa96ba1"
c87a95dc28b1 dm crypt: defer decryption to a tasklet if interrupts disabled
8e14f610159d dm crypt: do not call bio_endio() from the dm-crypt tasklet
d68b29584c25 dm crypt: use GFP_ATOMIC when allocating crypto requests from softirq
8abec36d1274 dm crypt: do not wait for backlogged crypto request completion in 
softirq
4a5caa4af0df dm crypt: document new no_workqueue flags

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