Re: increasing scsi_max_sg / max_segments for scsi writes/reads

From: sai narasimhamurthy (sai_narasi_at_yahoo.com)
Date: 04/18/05

  • Next message: Allison: "Kernel page table and module text" 
    Date:	Sun, 17 Apr 2005 23:17:23 -0700 (PDT)
To: "Randy.Dunlap" <rddunlap@osdl.org>

    Hi ,
    I tried working on scsi_malloc to increase burst size
    , but to no avail ..all I got was hanged system every
    time I started data transfers!
    Has anyone worked on scsi_malloc , I am still trying
    to figure out what changes were made in 2.6 to
    overcome this problem of limited bursts.

    Any pointers are very greatly welcome...I have never
    worked on this part of the code before .

    Sai

    --- "Randy.Dunlap" <rddunlap@osdl.org> wrote:
    > On Sat, 9 Apr 2005 19:35:52 -0700 (PDT) sai
    > narasimhamurthy wrote:
    >
    > | Hi,
    > | I had posted a question on increasing the scsi
    > | read/write sectors per command. I figured out
    > some of
    > | the things, but many questions still exist.
    > |
    > | I was wondering why the maximum writes I could get
    > | from a single scsi write command could never
    > exceed
    > | 204
    > | 4096B segments . I traced it to :
    > |
    > | static const int scsi_max_sg = PAGE_SIZE /
    > | sizeof(struct scatterlist)
    > |
    > | in scsi_merge.c .(which amounts to 204)
    > |
    > | Is this the limit of the maximum blocks we can
    > | read/write through a single scsi command, atleast
    > for
    > | the given kernel (2.4.29) ? How can I increase
    > | it??????
    > |
    > | I am on a P3 Dell poweredgde 2400 .
    >
    > Did you read the comment immediately above that
    > calculation?
    >
    > /*
    > * scsi_malloc() can only dish out items of
    > PAGE_SIZE or less, so we cannot
    > * build a request that requires an sg table
    > allocation of more than that.
    > */
    >
    > so scsi_malloc() would need some reworking to handle
    > more.
    >
    > OTOH, it appears that this is all removed in
    > 2.6.10++, so moving to
    > 2.6.recent is probably your best choice.
    >
    > ---
    > ~Randy
    > -
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