Re: usage of max_sectors in scsi_host_template
Erez Zilber wrote: I'm running sgp_dd (on RHAS 4 up4 - kernel version is 2.6.9), so it calls scsi-ml directly (without going through ll_rw_blk). ... I guess that the max_sectors value is never used. Am I right? I have no idea. However you might be able to track how max_sectors trickles through the layers via LXR: http://lxr.free-electrons.com/ident?i=max_sectors (Not all of the LXR sites out there support search for struct members but free-electrons' does.) -- Stefan Richter -=-=-=== =-== --=== http://arcgraph.de/sr/ - To unsubscribe from this list: send the line unsubscribe linux-scsi in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: usage of max_sectors in scsi_host_template
Stefan Richter wrote: Erez Zilber wrote: I'm not sure that I understand the meaning of max_sectors in scsi_host_template. Did you have a look at scsi_mid_low_api.txt? http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/scsi/scsi_mid_low_api.txt;h=6f70f2b9327e1f0db7bc05bdbf2d6ce3b2fcbdcf#l1232 I will go over it. Thanks for the link. Is it the maximum data length of a single SCSI command? Yes. Is it in bytes? No, it is in units of 512 bytes. What's the size of a sector? Usually 512 bytes according to above doc. Always 512 bytes from the point of view of block/ll_rw_blk.c::blk_queue_max_sectors(). http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=block/ll_rw_blk.c;h=75c98d58f4ddf7252e2717e0924b9d6a8925b4e5#l590 So, ll_rw_blk actually uses the max_sectors value to chop requests larger than max_sectors. Am I right? If yes, I have a problem: I'm running sgp_dd (on RHAS 4 up4 - kernel version is 2.6.9), so it calls scsi-ml directly (without going through ll_rw_blk). I ran it with the following parameters: sgp_dd bs=512 of=/dev/null if=/dev/sg1 bpt=2048 thr=4 time=1 count=100k deb=9 I see that a single 1MB command is generated. Here's the debug info from sgp_dd: sgp_dd: if=/dev/sg1 skip=0 of=/dev/null seek=0 count=102400 Start of loop, count=102400, in_num_sect=0, out_num_sect=0 Starting worker thread k=0 sg_start_io: SCSI READ, blk=0 num_blks=2048 Read (10) [28 00 00 00 00 00 00 08 00 00 ] dir=-3, len=1048576, dxfrp=0x2a9558a000, cmd_len=10 Now, the low-level driver below scsi-ml is open-iscsi over iSER. max_sectors is set to 1024 (i.e. 512 kB). Still, the iSER driver receives a 1MB command. I guess that the max_sectors value is never used. Am I right? Thanks, Erez - To unsubscribe from this list: send the line unsubscribe linux-scsi in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: usage of max_sectors in scsi_host_template
Erez Zilber wrote: Stefan Richter wrote: Erez Zilber wrote: I'm not sure that I understand the meaning of max_sectors in scsi_host_template. Did you have a look at scsi_mid_low_api.txt? http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/scsi/scsi_mid_low_api.txt;h=6f70f2b9327e1f0db7bc05bdbf2d6ce3b2fcbdcf#l1232 I will go over it. Thanks for the link. Is it the maximum data length of a single SCSI command? Yes. Is it in bytes? No, it is in units of 512 bytes. What's the size of a sector? Usually 512 bytes according to above doc. Always 512 bytes from the point of view of block/ll_rw_blk.c::blk_queue_max_sectors(). http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=block/ll_rw_blk.c;h=75c98d58f4ddf7252e2717e0924b9d6a8925b4e5#l590 So, ll_rw_blk actually uses the max_sectors value to chop requests Well, there is q-max_sectors and q-max_hw_sectors. In current kernels q-max_hw_sectors is scsi_host_template-max_sectors. And q-max_sectors is sort of a block layer limit to make sure commands to not get too big. larger than max_sectors. Am I right? If yes, I have a problem: I'm running sgp_dd (on RHAS 4 up4 - kernel version is 2.6.9), so it calls scsi-ml directly (without going through ll_rw_blk). I ran it with the following parameters: RHEL4's sg.c does not take into account q-max_sectors or q-max_hw_sectors. In later kernels like in RHEL5 (probably upstream 2.6.16+), sg.c and st.c goes through llw_rw_blkc and obeys the sector limit. For pass through like sg and block layer sg, the scsi command is limited by q-max_hw_sectors which like I said above is scsi_host_template-max_sectors. And normal FS commands are limited by min(q-max_hw_sectors, q-max_sectors). - To unsubscribe from this list: send the line unsubscribe linux-scsi in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
usage of max_sectors in scsi_host_template
I'm not sure that I understand the meaning of max_sectors in scsi_host_template. Is it the maximum data length of a single SCSI command? Is it in bytes? What's the size of a sector? Thanks, -- Erez Zilber | 972-9-971-7689 Software Engineer, Storage Solutions Voltaire – _The Grid Backbone_ __ www.voltaire.com http://www.voltaire.com/ - To unsubscribe from this list: send the line unsubscribe linux-scsi in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: usage of max_sectors in scsi_host_template
Erez Zilber wrote: I'm not sure that I understand the meaning of max_sectors in scsi_host_template. Did you have a look at scsi_mid_low_api.txt? http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=Documentation/scsi/scsi_mid_low_api.txt;h=6f70f2b9327e1f0db7bc05bdbf2d6ce3b2fcbdcf#l1232 Is it the maximum data length of a single SCSI command? Yes. Is it in bytes? No, it is in units of 512 bytes. What's the size of a sector? Usually 512 bytes according to above doc. Always 512 bytes from the point of view of block/ll_rw_blk.c::blk_queue_max_sectors(). http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=blob;f=block/ll_rw_blk.c;h=75c98d58f4ddf7252e2717e0924b9d6a8925b4e5#l590 -- Stefan Richter -=-=-=== =-== --==- http://arcgraph.de/sr/ - To unsubscribe from this list: send the line unsubscribe linux-scsi in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
