ACK: [PATCH 0/2][SRU][E] improve ext4 performance with revert of a reverted ext4 fix

[Andrea Righi]

On Thu, Oct 03, 2019 at 02:10:02PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1846486
> 
> == SRU Justification Eoan ==
> 
> Now that 5.4 contains a fix to the bootup regression due to the
> lack of entropy at bootable we should apply this fix and also
> revert the revert of commit 
> "Revert "ext4: make __ext4_get_inode_loc plug"".
> 
> == Fix ==
> 
> So, to clarify, apply the two upstream 5.4-rc commits:
> 
> commit 50ee7529ec4500c88f8664560770a7a1b65db72b
> Author: Linus Torvalds <torvalds at linux-foundation.org>
> Date: Sat Sep 28 16:53:52 2019 -0700
> 
>     random: try to actively add entropy rather than passively wait for it
> 
> commit 02f03c4206c1b2a7451d3b3546f86c9c783eac13
> Author: Linus Torvalds <torvalds at linux-foundation.org>
> Date: Sun Sep 29 17:59:23 2019 -0700
> 
>     Revert "Revert "ext4: make __ext4_get_inode_loc plug""
> 
> I've benchmarked the Eoan kernel with these two patches and found theo
> following speed improvements on an i7-3770 CPU @ 3.40GHz with 8GB and a
> WDC WD10EZEX-21WN4A HDD (7200RPM, 64MB cache).
> 
> git grep of the kernel: 0.14%
> building fwts: 0.40%
> build stress-ng 0.45%
> tar up kernel source: 7.6%
> boot time of eoan cloud image: 10.5% 
> 
> So I think the speed improvements justifies the SRU.
> 
> == Regression potential ==
> 
> Minor change to ext4, which has been regression tested, so risk here is
> small. The entropy change will alter the random number generation, but
> I believe this does not change the cryptographical security of the random
> numbers being generated, so think this change is not security risk.
> 
> Originally the ext4 change caused boot time user space regressions
> because of the entropy change of this fix, but the random fix addresses
> this, so I believe this risk is now zero.
> 
> Linus Torvalds (2):
>   random: try to actively add entropy rather than passively wait for it
>   Revert "Revert "ext4: make __ext4_get_inode_loc plug""
> 
>  drivers/char/random.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++-
>  fs/ext4/inode.c       |  3 +++
>  2 files changed, 64 insertions(+), 1 deletion(-)

I followed this thread on the LKML. :) I think it's very reasonable to
apply it, therefore:

Acked-by: Andrea Righi <andrea.righi at canonical.com>