This week attended a webinar from Alex Blewitt about CPU microarchiteture to increase application performance. The link was sent by a work colleague but you can get pdf and see the presentation from the below source:


The presentation is obviously very interesting. You need to know your CPU to get the most of it.

How can I see my CPU architecture? “lstopo” (graphic) or “lstopo-no-graphics” is your friend. This is from my laptop.

# lstopo-no-graphics
Machine (7934MB total)
Package L#0
NUMANode L#0 (P#0 7934MB)
L3 L#0 (4096KB)
L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0
PU L#0 (P#0)
PU L#1 (P#2)
L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1
PU L#2 (P#1)
PU L#3 (P#3)
PCI 00:02.0 (VGA)
PCI 02:00.0 (Network)
Net "wlp2s0"
PCI 00:1f.2 (SATA)
Block(Disk) "sda"

As you can see, my humble laptop just have one NUMA node, with two cores/processors, and two hyperthreads per core.

But in a server, very likely you will have more NUMA nodes, more cores and more processors so you want to be sure that is used properly.

I am not expert in CPU performance at all but there many important points like memory allocation, huge pages, pinning memory/threads (isolcpu, taskset, etc), compiler strategies and tools to test the performance. Some of them ring the bell and it is nice to know that exist. You never know when you will have to dive in this type of water.

LVM 101 + Linux disk encryption

Once more post from Cloudflare. I think most Linux distributions already offer by default transparent disk encryption. As far as I can see in my Debian, I have encryption with LVM. I need to write a post about LVM as I have always to google most basic command. “Logic Volume Manager” (LVM) is an abstraction layer for managing storage (maybe too basic explanation but that is how I understand it). When I built my laptop, I had the option (I think it was by default) to choose LVM + encryption (dm_crypt module). So I took that.

So first, how I check my LVM? Well, df -h, will give the first clues

# df -hT
Filesystem Type Size Used Avail Use% Mounted on
udev devtmpfs 3.9G 0 3.9G 0% /dev
tmpfs tmpfs 794M 2.7M 791M 1% /run
/dev/mapper/laptop--vg-root ext4 24G 17G 6.3G 73% /
tmpfs tmpfs 3.9G 414M 3.5G 11% /dev/shm
tmpfs tmpfs 5.0M 8.0K 5.0M 1% /run/lock
tmpfs tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/sda2 ext2 237M 155M 70M 69% /boot
/dev/sda1 vfat 496M 60M 437M 13% /boot/efi
/dev/mapper/laptop--vg-home ext4 20G 9.9G 8.7G 54% /home
tmpfs tmpfs 794M 24K 794M 1% /run/user/1000

You see thing with “/dev/mapper” and “vg” (volume group). So you have LVM running.

Some basic LVM notes:

# pvs –> it will show the physical disks, partitions, etc used in your LVM setup and the “vgs” they belong to. PVS stands for “physical volume system”. In my case only the partition sda3 from my physical disk is part of LVM. Physical volumes are used to create Volume groups.

# pvs
PV VG Fmt Attr PSize PFree
/dev/mapper/sda3_crypt laptop-vg lvm2 a-- 237.73g <2.62g

# vgs –> it will show you the volumes in your system, the number of PV they are using and the number of LV they are providing. VGS stands for “volume group system”. In my case, I have just one VG, that is use 1 PV and is providing 4 LV.

# vgs
VG #PV #LV #SN Attr VSize VFree
laptop-vg 1 4 0 wz--n- 237.73g <2.62g

#lvs –> it will show the “logical volumes” you have created from a VG. In my case, I have four LV.

# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
home laptop-vg -wi-ao---- 22.00g
root laptop-vg -wi-ao---- 24.31g
storage laptop-vg -wi-ao---- 182.00g
swap_1 laptop-vg -wi-ao---- 6.80g

BTW, how I can see all the partitions in my machine, “fdisk -l”

root@athens:/boot# fdisk -l
Disk /dev/sda: 238.49 GaiB, 256060514304 bytes, 500118192 sectors
Disk model: NISU SSD ALLI
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Device Start End Sectors Size Type
/dev/sda1 2048 1050623 1048576 512M EFI System
/dev/sda2 1050624 1550335 499712 244M Linux filesystem
/dev/sda3 1550336 500117503 498567168 237.8G Linux filesystem

So based on our “pvs” we know “dev/sda3” is part of LVM. How the encryption is happening? The type of partition will tell us

# blkid /dev/sda3
/dev/sda3: UUID="f6263aee-3966-4c23-a4ef-b4d9916f1a07" TYPE="crypto_LUKS" PARTUUID="b224eb49-1e71-4570-8b62-fb38df801170"

So, “crypto_LUKS” is key. Our LVM is running over a partition that is encrypted.

So after this detour, lets go back to Cloudflare post about Linux disk encryption.

I really enjoyed the kind of forensic work trying to discover when and why the changes in the Linux kernel code (!) were happening and how affected the speed. BTW, I crashed my laptop when trying to run their tests!


Iptables Conntrack

I am subscribed to Cloudflare blog as they are in general really good. And definitely, you always learn something new (and want to cry because you have so much to learn from these guys).

This time was a dissection of conntrack in iptables to improve their firewall performance.


I never thought about the limits of the conntrack table and how important is to have in mind (or make a tattoo of) the iptables diagram.

Ensaladilla Rusa (Russian Salad)

This blog is mainly for “Today I learned…” (TIL). And that can be anything…. so don’t get surprised. It could be worse ™

“Ensaladilla Rusa” (Russian Salad) is a typical Spanish dish. I remember we had it nearly every week in summer time. With the hot weather, having something fresh, it was a bless. Like “gazpacho” 🙂

But I have never tried it on my own until last weekend. I love cooking (I dont consider myself a good cook though), it is relaxing and I regard it as a very important part of my upbringing and culture. I want to keep it and enjoy it! It has to be simple, humble, tasty, etc. Dont like fancy or over the top things.

So back to the track… You can find many recipes in google/youtube, it is like “Tortilla Española”, each home has its own. This is the one I tried and I liked the result:

Ingredients for the salad

  • 1kg potatoes
  • 500g of frozen vegetables mix (peas, carrots, corn, beans)
  • 1 can of tuna (or 2)
  • 4 boiled eggs (salt and vinegar in the water so the shell doesn’t break)

Ingredient for the mayonesse

  • 1 egg
  • salt
  • juice of 1/2 lemon (you will have to taste and maybe you dont need to use all of it)
  • 500ml oil (I mixed 250ml sunflower oil + 250ml virgin olive oil)


  • Boil the potatoes with enough water and salt (skin included). Be sure the potatoes are similar size so the go tender around the same time. Cut them if needed. They are ready when you can cross a knife through the potato without effort. This is not mash potatoes though 🙂 Let them cool down
  • I put the frozen salad in boiling water for 1-2 minutes so they became eatable again.
  • Boil the eggs with enough water (salt and vinegar). Around 10 minutes. Let cool down a bit under a bit of cold water. Then remove the shell (it shouldn’t be too difficult) and cut them in small cubes.
  • Peel the potatoes with your hand and cut them in little cubes (like the eggs)
  • In a glass try, mix the potatoes, vegetables, eggs and tuna. Let them cool in the fridge.
  • Once you get your mayonnaise, add it to the mix. Cool a bit in the fridge and ready to eat!

Mayonnaise Process:

  • Put in your hand mixer glass, the egg, salt, some lemon juice and a bit of oil to cover the mixer head.
  • Start mixing and it will become white. Then start adding the rest of oil bit a bit.
  • The mix shouldn’t be liquid neither solid. Something like heavier egg whites.
  • Taste it, very important. Add more salt? More lemon? Mine had a strong lemony flavour but remember you will add it to the salad.
  • Ready to use with the salad.

Shito Ryu – Remembering

Somehow today while working out at home, paid attention to my old black belt and crossed my mind that I could try to remember some of my old Karate. It has been a long time since I donned my kimono and I am supper rusty but I did it. It was really special, so many old memories. I remembered how to wear it and how to put the belt! So many years grinning have paid off 🙂

I was pretty sure I could find videos of my Karate style Shito Rye in Youtube and quickly found a good one:


Funny enough I could remember most of the moves. So my goal it is to practice a bit every day.


I have been practising all lock-down weeks so I am quite happy. Adding new katas:

Shito-Ryu Kata – Matsukaze

SSH Keys

I already use RSA ssh keys to access my VPS but a friend of mine send me a link about ED25519 public-key algorithm. But why ssh-keys? Mainly to avoid to type your password every single time.


I will not explain the maths behind because I can’t (but I would love to understand) so wikipedia can do a better work (and in the main time, think of donating a few bucks 🙂


If you still want to generate RSA keys (you can have both), this is my go-to link:


Summary, just in case the links disappear:

# create your key RSA or Ed25519

$ ssh-keygen -t rsa -f ~/.ssh/id_rsa4096 -b 4096 -C "user@origin"


$ ssh-keygen -o -a 100 -t ed25519 -f ~/.ssh/id_ed25519 -C "user@origin"

# Add your priv key into your ssh-agent so it is used when connecting to the destination

$ ssh-add ~/.ssh/id_xxx

# Copy your PUBLIC!!! key to the remote server you want to login with that key (and so you dont need to type a password)

$ ssh-copy-id -i .ssh/id_xxx.pub user@remove_server

# Test your new ssh-key

$ ssh -i ~/.ssh/id_xxx user@remove_server

Linux Network Namespaces

At work, we use a vendor whose Network Operating System (NOS) is based in Linux. I am a network engineer so I was troubleshooting an issue inside a VRF. I couldn’t use much of the normal commands in the default VRF. So I opened a ticket with the vendor and learned a bit how the VRFs are implemented under the hoods. Obviously (not for me) they use Linux Namespaces, after googling the meaning of the commands they sent. My search brought me to the following links:

This is a good intro:


From this link, I took some examples in my quick search


At the end I used commands like these:

$ sudo ip netns list
$ sudo ip netns exec ns-INET ip link list
$ sudo ip netns exec ns-VRF1 arp -a
$ sudo ip netns exec ns-VRF1 route -n
$ sudo ip netns exec ns-VRF1 telnet -b src_ip dst_ip port
$ sudo ip netns exec ns-VRF1 tcpdump -i lo4 -nn  tcp 179
$ sudo ip netns exec ns-VRF1 ss --tcp --info
$ sudo ip netns exec ns-VRF1 ss --tcp --info -nt src IP

As well, “ss” is such a useful command for troubleshooting and I always feel that I dont make the most of it: