[lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)

Pinkesh Valdria pinkesh.valdria at oracle.com
Wed Dec 11 08:45:57 PST 2019

I was not able to find those parameters on my client nodes,  OSS or MGS nodes.   Here is how I was extracting all parameters .  


mkdir -p lctl_list_param_R/

cd lctl_list_param_R/

lctl list_param -R *  > lctl_list_param_R


[opc at lustre-client-1 lctl_list_param_R]$ less lctl_list_param_R  | grep ahead







[opc at lustre-client-1 lctl_list_param_R]$


I also tried these commands:  


Not working: 

On client nodes

lctl get_param llite.lfsbv-*.max_read_ahead_mb

error: get_param: param_path 'llite/lfsbv-*/max_read_ahead_mb': No such file or directory

[opc at lustre-client-1 lctl_list_param_R]$



On client nodes

lctl get_param llite.*.statahead_agl



[opc at lustre-client-1 lctl_list_param_R]$




From: "Moreno Diego (ID SIS)" <diego.moreno at id.ethz.ch>
Date: Tuesday, December 10, 2019 at 2:06 AM
To: Pinkesh Valdria <pinkesh.valdria at oracle.com>, "lustre-discuss at lists.lustre.org" <lustre-discuss at lists.lustre.org>
Subject: Re: [lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)


With that kind of degradation performance on read I would immediately think on llite’s max_read_ahead parameters on the client. Specifically these 2:


max_read_ahead_mb: total amount of MB allocated for read ahead, usually quite low for bandwidth benchmarking purposes and when there’re several files per client

max_read_ahead_per_file_mb: the default is quite low for 16MB RPCs (only a few RPCs per file)


You probably need to check the effect increasing both of them.







From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of Pinkesh Valdria <pinkesh.valdria at oracle.com>
Date: Tuesday, 10 December 2019 at 09:40
To: "lustre-discuss at lists.lustre.org" <lustre-discuss at lists.lustre.org>
Subject: [lustre-discuss] Degraded read performance with Large Bulk IO (16MB RPC)


I was expecting better or same read performance with Large Bulk IO (16MB RPC),  but I see degradation in performance.   Do I need to tune any other parameter to benefit from Large Bulk IO?   Appreciate if I can get any pointers to troubleshoot further. 


Throughput before 

-          Read:  2563 MB/s

-          Write:  2585 MB/s


Throughput after

-          Read:  1527 MB/s. (down by ~1025)

-          Write:  2859 MB/s



Changes I did are: 

On oss

-          lctl set_param obdfilter.lfsbv-*.brw_size=16


On clients 

-          unmounted and remounted

-          lctl set_param osc.lfsbv-OST*.max_pages_per_rpc=4096  (got auto-updated after re-mount)

-          lctl set_param osc.*.max_rpcs_in_flight=64   (Had to manually increase this to 64,  since after re-mount, it was auto-set to 8,  but read/write performance was poor)

-          lctl set_param osc.*.max_dirty_mb=2040. (setting the value to 2048 was failing with : Numerical result out of range error.   Previously it was set to 2000 when I got good performance. 



My other settings: 

-          lnetctl net add --net tcp1 --if $interface  –peer-timeout 180 –peer-credits 128 –credits 1024

-          echo "options ksocklnd nscheds=10 sock_timeout=100 credits=2560 peer_credits=63 enable_irq_affinity=0"  >  /etc/modprobe.d/ksocklnd.conf

-          lfs setstripe -c 1 -S 1M /mnt/mdt_bv/test1


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